Fix location of GPT header on 4K LBA devices.

BUG: 453333

src/plugins/sfdisk/sfdiskbackend.cpp

@@ -451,7 +451,8 @@ bool SfdiskBackend::updateDevicePartitionTable(Device &d, const QJsonObject &jso
         // Read the maximum number of GPT partitions
         qint32 maxEntries;
         QByteArray gptHeader;
-        CopySourceDevice source(d, 512, 1023);
+        qint64 sectorSize = d.logicalSize();
+        CopySourceDevice source(d, sectorSize, sectorSize * 2 - 1);
 
         ExternalCommand readCmd;
         gptHeader = readCmd.readData(source);