Since objectName() isn't always set, the className() makes it slightly
easier to find and fix the issue.
Also unify some wording "produce a warning", which is generic enough to
fit:
print warning in terminal
print warning in logviewer (if you're unlucky and have to use Windows?)
print warning in system journal (if you're unlucky have to use binary
systemd journal logs)
Pick-to: 6.4
Change-Id: I7522d65666cb5829c33c45039b8646dd535e21ea
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
60c69b4da5