Fix imported file score path

importedFilePath should be empty for not imported files. I checked as Marc suggested - and it was always set to score name. 
It was supposed to set only for midi, kar, ... files - not score files.

Also there should be score->importedFilePath() != score->fileInfo()->canonicalFilePath()
in any case.

So very likely it IS a fix or one of the fixes for http://musescore.org/en/node/41251.

But the check from somebody else would be useful.