Don't unnecessarily stop the ShareActivity in onPause.

1. Due to ShareActivity having noHistory=true, it will already be
ditched when you leave the activity.
2. We only need to truly finish() here if we've dropped the underlying
media.

Fixes #8591

src/org/thoughtcrime/securesms/ShareActivity.java

@@ -133,11 +133,12 @@ public class ShareActivity extends PassphraseRequiredActionBarActivity
     super.onPause();
     if (!isPassingAlongMedia && resolvedExtra != null) {
       PersistentBlobProvider.getInstance(this).delete(this, resolvedExtra);
-    }
+
       if (!isFinishing()) {
         finish();
       }
     }
+  }
 
   @Override
   public void onBackPressed() {