Replace OSL_VERIFY with SAL_WARN_IF and add some unit tests to ensure
the replacements don't some side effects.

Change-Id: I96eb00e2856e767e83596a21d30ae12a0efddf6d
Reviewed-on: https://gerrit.libreoffice.org/71252
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>