Check readVariableByteInteger() return value


- On error, readVariableByteInteger() closes the connection and
returns-1. In this case, message handling should stop.

- Add checks for the return value to stop processing when -1 is returned.

Pick-to: 6.11 6.8 6.12
Task-number: QTBUG-149565
Change-Id: I8f6cc8d6f3011a89d3bd4033a3432f383e1e9164
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
commit13288574c1db277899eb7c917373669a6720b9b3
parentecaf42152efc474cfdcfbefc253e40e7626bd6c1
authorTatiana Borisova <tatiana.borisova@qt.io>
committerTatiana Borisova <tatiana.borisova@qt.io>
commit timeFri, 28 Aug 2026 12:07:30 +0000