Incorrect check for CamelSettings value change

Incorrect check for CamelSettings value change

This was causing runtime warnings on evolution start from IMAP provider,
which reads values from settings for junk/trash real folder, but
the settings object was set as NULL, which means "create default settings
for this class", but the test I added for object pointer change did
succeed for the NULL object (both internal and passed in settings are NULL
at the beginning), thus the default settings object was not created.