[BndEditor] Fix resource check on attempt to resolve
[BndEditor] Fix resource check on attempt to resolve

Previous check had the polarity reversed from what it should have been,
and also failed silently when the check failed. These changes fix the
polarity and also announce the failure to the user via a messagebox.

Fixes #3791.

Signed-off-by: Fr Jeremy Krieg <f86269a0d7ab2c7f993321a0ff17f12406f20621@greekwelfaresa.org.au>

psoreide/bnd,psoreide/bnd,psoreide/bnd