ref(conference.js): show screensharing error first

If there will be microphone error it will cover any screensharing
dialog, but it's still better than in the reverse order where
the screensharing dialog will sometime be closing the microphone alert
($.prompt.close(); is called).

conference.js

             .then(([tracks, con]) => {
                 APP.store.dispatch(
                     mediaPermissionPromptVisibilityChanged(false));
+                // FIXME If there will be microphone error it will cover any
+                // screensharing dialog, but it's still better than in
+                // the reverse order where the screensharing dialog will
+                // sometime be closing the microphone alert ($.prompt.close();
+                // is called). Need to figure out dialogs chaining to fix that.
+                if (screenSharingError) {
+                    this._handleScreenSharingError(screenSharingError);
+                }
                 if (audioAndVideoError || audioOnlyError) {
                     if (audioOnlyError || videoOnlyError) {
                         // If both requests for 'audio' + 'video' and 'audio'
                     }
                 }
 
-                // FIXME If there was a screen sharing error or the extension
-                // needs to be installed it will appear on top of eventual
-                // "microphone error" dialog. That is not great, but currently
-                // it's pretty hard to chain dialogs since they don't return
-                // Promises.
-                if (screenSharingError) {
-                    // FIXME if _handleScreenSharingError will be dealing with
-                    // installing external extension it may close previously
-                    // opened microphone dialog ($.prompt.close(); is called).
-                    this._handleScreenSharingError(screenSharingError);
-                }
-
                 return [tracks, con];
             });
     },