Merge pull request #819 from react-native-webrtc/enforce_one_looper

Enforce one looper for telephony listener

Author: manuquentin

android/src/main/java/io/wazo/callkeep/RNCallKeepModule.java

@@ -318,7 +318,9 @@ public void listenToNativeCallsState() {
                   callStateListener = new CallStateListener();
                   telephonyManager.registerTelephonyCallback(context.getMainExecutor(),callStateListener);
             } else {
-                  Looper.prepare();
+                  if (Looper.myLooper() == null) {
+                    Looper.prepare();
+                  }
                   legacyCallStateListener  = new LegacyCallStateListener();
                   telephonyManager.listen(legacyCallStateListener, PhoneStateListener.LISTEN_CALL_STATE);
                   Looper.loop();