feat: add an isVisisble check before opening the camera

This is another measure to prevent the event from making multiple opened compose screens (like when you click on a notification when you are already replying to someone) open the camera at the same time and add a repeated attachment to all opened compose screens

mastodon/src/main/java/org/joinmastodon/android/fragments/ComposeFragment.java

@@ -1461,6 +1461,7 @@ public class ComposeFragment extends MastodonToolbarFragment implements OnBackPr
 
 	@Subscribe
 	public void onTakePictureRequest(TakePictureRequestEvent ev){
+		if(isVisible())
 			openCamera();
 	}