Return empty value for non-existing UIC 918.3 blocks

This prevents JS extractor scripts from accidentally accessing an invalid
block object.

src/lib/uic9183/uic9183parser.cpp

@@ -67,21 +67,20 @@ QVariant Uic9183Parser::block(const QString &name) const
         return {};
     }
 
-    if (name == QLatin1String(Uic9183Head::RecordId)) {
-        return QVariant::fromValue(findBlock<Uic9183Head>());
-    }
-    if (name == QLatin1String(Uic9183TicketLayout::RecordId)) {
-        return QVariant::fromValue(ticketLayout());
-    }
-    if (name == QLatin1String(Fcb::UicRailTicketData::RecordId)) {
-        return QVariant::fromValue(findBlock<Fcb::UicRailTicketData>());
-    }
-    if (name == QLatin1String(Vendor0080BLBlock::RecordId)) {
-        return QVariant::fromValue(findBlock<Vendor0080BLBlock>());
-    }
-    if (name == QLatin1String(Vendor0080VUBlock::RecordId)) {
-        return QVariant::fromValue(findBlock<Vendor0080VUBlock>());
+#define BLOCK_FROM_NAME(Type) \
+    if (name == QLatin1String(Type::RecordId)) { \
+        const auto block = findBlock<Type>(); \
+        return block.isValid() ? QVariant::fromValue(block) : QVariant(); \
     }
+
+    BLOCK_FROM_NAME(Uic9183Head)
+    BLOCK_FROM_NAME(Uic9183TicketLayout)
+    BLOCK_FROM_NAME(Fcb::UicRailTicketData)
+    BLOCK_FROM_NAME(Vendor0080BLBlock)
+    BLOCK_FROM_NAME(Vendor0080VUBlock)
+
+#undef BLOCK_FROM_NAME
+
     return QVariant::fromValue(findBlock(name.toUtf8().constData()));
 }
 

src/lib/uic9183/vendor0080block.cpp

@@ -233,7 +233,7 @@ Vendor0080BLSubBlock Vendor0080BLBlock::findSubBlock(const char id[3]) const
 
 QVariant Vendor0080BLBlock::findSubBlock(const QString &str) const
 {
-    if (str.size() != 3) {
+    if (str.size() != 3 || !isValid()) {
         return {};
     }
     const auto b = findSubBlock(str.toUtf8().constData());