android: make sure we left the current meeting when the activity is destroyed

If the user swipes the activity from the recents list there is no other chance,
onDestroy gets called directly.

android/sdk/src/main/java/org/jitsi/meet/sdk/JitsiMeetActivity.java

@@ -71,6 +71,13 @@ public class JitsiMeetActivity extends FragmentActivity
         }
     }
 
+    @Override
+    public void onDestroy() {
+        leave();
+
+        super.onDestroy();
+    }
+
     @Override
     public void finish() {
         leave();