FileManager backend:fix 2 b0rks related to getMimeTypeDefintions(): code error and cope when the specified mapping file is bogus or non-existent.
FileManager backend:fix 2 b0rks related to getMimeTypeDefintions(): code error and cope when the specified mapping file is bogus or non-existent.

cpojer/mootools-filemanager,cpojer/mootools-filemanager