CAN: Reject out-of-range signal and message fields in DBC parser

extractSignal() and extractMessage() narrow the numeric DBC fields to
quint16 and quint8 with no range check, so a file could place a signal
wholly outside its message and still produce a valid-looking
description, leaving the codec bounds check as the only defence.

Range-check before narrowing and skip the offending signal or message
with a warning, matching the existing addWarning() pattern, so one bad
line does not fail the file.

Patch created with the help of Claude Opus 5, based on a deep-scan that
got concluded on this repository. Verified and corrected by myself.

Fixes: QTBUG-149967
Pick-to: 6.12 6.12.0 6.11 6.11.3 6.10 6.8
Change-Id: Id73f478cb0e336d813ef84a069115c8e285c1635
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>