ok 141 - convert_datetime doesn't blow up if sent bogus date
Invalid date format:  at /path/to/MyApp/Util.pm line 818.
	eval {...} called at /path/to/MyApp/Util.pm line 818
	MyApp::Util::convert_datetime("MyApp::Util", "FOO") called at t/Util.t line 297
	...propagated at t/Util.t line 298.