Fix parsing of BCBPs that claim to have a zero-length conditioanl block

Found e.g. in some Qatar Airways boarding passes.

autotests/bcbpdata/qatar-zero-size-conditional-section.json

+[
+    {
+        "@context": "http://schema.org",
+        "@type": "FlightReservation",
+        "airplaneSeat": "42F",
+        "passengerSequenceNumber": "23",
+        "reservationFor": {
+            "@type": "Flight",
+            "airline": {
+                "@type": "Airline",
+                "iataCode": "QR"
+            },
+            "arrivalAirport": {
+                "@type": "Airport",
+                "iataCode": "DOH"
+            },
+            "departureAirport": {
+                "@type": "Airport",
+                "iataCode": "MXP"
+            },
+            "departureDay": "2018-09-13",
+            "flightNumber": "128"
+        },
+        "reservationNumber": "XXX007",
+        "reservationStatus": "http://schema.org/ReservationConfirmed",
+        "reservedTicket": {
+            "@type": "Ticket",
+            "ticketToken": "aztecCode:M1DOE/JANE            EXXX007 MXPDOHQR 0128 256Y042F0023 100>2180  0255BBR              2963456000789980                            0"
+        },
+        "underName": {
+            "@type": "Person",
+            "familyName": "DOE",
+            "givenName": "JANE"
+        }
+    }
+]

autotests/bcbpdata/qatar-zero-size-conditional-section.txt

+IATA Barcoded Boarding Pass
+formatCode: M
+numberOfLegs: 1
+passengerName: DOE/JANE
+electronicTicketIndicator: E
+version: 0
+fieldSize: 0
+passengerDescription: 
+sourceOfCheckin: 
+sourceOfBoardingPassIssuance: 
+yearOfIssue: 0
+dayOfIssue: 0
+documentType: 
+airlineDesignatorOfBoardingPassIssuer: 
+baggageTagLicensePlateNumber1: 
+baggageTagLicensePlateNumber2: 
+baggageTagLicensePlateNumber3: 
+Date of issue: 
+Leg 1
+  operatingCarrierPNRCode: XXX007
+  fromCityAirportCode: MXP
+  toCityAirportCode: DOH
+  operatingCarrierDesignator: QR
+  flightNumber: 0128
+  dayOfFlight: 256
+  compartmentCode: Y
+  seatNumber: 042F
+  checkinSequenceNumber: 0023
+  passengerStatus: 1
+  variableFieldSize: 0
+  conditionalFieldSize: 0
+  airlineNumericCode: 
+  documentNumber: 
+  selecteeIndicator: 
+  internationalDocumentVerification: 
+  marketingCarrierDesignator: 
+  frequentFlyerAirlineDesignator: 
+  frequenFlyerNumber: 
+  idAdIndicator: 
+  freeBaggageAllowance: 
+  fastTrack: 
+  Airline use section: 
+  Date of flight: 2018-09-13

autotests/bcbpparsertest.cpp

@@ -55,6 +55,8 @@ private Q_SLOTS:
         // TAP missing boarding pass issue date
         QTest::newRow("no issue date") << QStringLiteral("M1DOE/JOHN            EXXX007 LISLCGTP 1080 204Y002D0003 35C>2180      B1A              2904712345678900                           *306      09     BRND") << QStringLiteral("tap-missing-issue-date");
 
+        // Qatar claiming zero-length field sizes
+        QTest::newRow("zero size conditional") << QStringLiteral("M1DOE/JANE            EXXX007 MXPDOHQR 0128 256Y042F0023 100>2180  0255BBR              2963456000789980                            0") << QStringLiteral("qatar-zero-size-conditional-section");
     }
 
     void testParserValid()
@@ -87,6 +89,9 @@ private Q_SLOTS:
         QCOMPARE(proc.exitCode(), 0);
         if (ticketDump != refOut) {
             qDebug().noquote() << ticketDump;
+            QFile failFile(ref.fileName() + QLatin1String(".fail"));
+            QVERIFY(failFile.open(QFile::WriteOnly));
+            failFile.write(ticketDump);
         }
         QVERIFY(ticketDump == refOut);
 
@@ -100,6 +105,9 @@ private Q_SLOTS:
 
         if (refArray != resJson) {
             qWarning().noquote() << QJsonDocument(resJson).toJson();
+            QFile failFile(f.fileName() + QLatin1String(".fail"));
+            QVERIFY(failFile.open(QFile::WriteOnly));
+            failFile.write(QJsonDocument(resJson).toJson());
         }
         QCOMPARE(resJson, refArray);
     }

src/lib/iata/iatabcbp.cpp

@@ -66,12 +66,17 @@ IataBcbpUniqueMandatorySection IataBcbp::uniqueMandatorySection() const
 
 bool IataBcbp::hasUniqueConditionalSection() const
 {
-    return (m_data.size() > (UniqueMandatorySize + RepeatedMandatorySize)) && (m_data.at(UniqueMandatorySize + RepeatedMandatorySize) == QLatin1Char('>'));
+    return (m_data.size() > (UniqueMandatorySize + RepeatedMandatorySize))
+        && (m_data.at(UniqueMandatorySize + RepeatedMandatorySize) == QLatin1Char('>'))
+        && repeatedMandatorySection(0).variableFieldSize() > MinimumUniqueConditionalSize;
 }
 
 IataBcbpUniqueConditionalSection IataBcbp::uniqueConditionalSection() const
 {
-    return IataBcbpUniqueConditionalSection(QStringView(m_data).mid(UniqueMandatorySize + RepeatedMandatorySize));
+    if (hasUniqueConditionalSection()) {
+        return IataBcbpUniqueConditionalSection(QStringView(m_data).mid(UniqueMandatorySize + RepeatedMandatorySize));
+    }
+    return IataBcbpUniqueConditionalSection(QStringView());
 }
 
 IataBcbpRepeatedMandatorySection IataBcbp::repeatedMandatorySection(int leg) const