added file exitence check before trying to detect its mime type using the file binary
added file exitence check before trying to detect its mime type using the file binary

git-svn-id: aca338ffdbd09f6633b51c659d43d692158a45c1@62 6fc1d829-d401-48c8-9a3f-03588956443c

xavierlacot/mediatorMediaLibraryPlugin,xavierlacot/mediatorMediaLibraryPlugin