adds full test for catching swf file in a theme and fixes possible warnings caused by empty css and php files
Adding a full test for swf files should help with test coverage of swf file test case as it is not checking only if check_filename function if WaD, but also is checking if BaseScanner object holds corrent error levels for the specified file.
As our testcase does not contain a php and css files, I had to sanitize a code of BaseScanner class which was raising a PHP Warning (and thus breaking the phpunit run) for unset array key - checking for issset is enaugh in this case. My patch also contains yoda conditons style which I find more fool proof while developing.