Don't crash if I click "cancel" in getOpenFileNames

modules/gui/qt4/dialogs_provider.cpp

@@ -309,7 +309,10 @@ void DialogsProvider::openFileGenericDialog( intf_dialog_args_t *p_arg )
         i = 0;
         foreach( const QString &file, files )
             p_arg->psz_results[i++] = strdup( qtu( toNativeSepNoSlash( file ) ) );
-        p_intf->p_sys->filepath = qfu( p_arg->psz_results[i] );
+        if(i == 0)
+            p_intf->p_sys->filepath = QString::fromAscii("");
+        else
+            p_intf->p_sys->filepath = qfu( p_arg->psz_results[i] );
     }
 
     /* Callback */