Import manager: Fixing false invalid file positive.

There is an highly chance of 0-lengthed images, as they don't have
length.

src/Gui/import/ImportController.cpp

@@ -231,7 +231,8 @@ ImportController::accept()
     collapseAllButCurrentPath();
     foreach ( Clip* clip, m_temporaryMedias->clips().values() )
     {
-        if ( clip->getMedia()->lengthMS() == 0 && clip->getMedia()->inputType() == Media::File )
+        if ( ( clip->getMedia()->lengthMS() == 0 && clip->getMedia()->fileType() != Media::Image ) &&
+             clip->getMedia()->inputType() == Media::File )
             invalidMedias = true;
         Library::getInstance()->addClip( clip );
     }