CallPresenter: fix NullPointerException

Change-Id: I7985c7adfd40760bc0c8f8f93dca3047720f6a1f

ring-android/libringclient/src/main/java/cx/ring/call/CallPresenter.java

@@ -560,7 +560,7 @@ public class CallPresenter extends RootPresenter<CallView> {
     }
 
     public void toggleButtonClicked() {
-        if (!(mConference.isRinging() && mConference.isIncoming())) {
+        if (mConference != null && !(mConference.isRinging() && mConference.isIncoming())) {
             hangupCall();
         }
     }

ring-android/libringclient/src/main/java/cx/ring/conversation/ConversationPresenter.java

@@ -319,7 +319,7 @@ public class ConversationPresenter extends RootPresenter<ConversationView> {
     }
 
     public void clickOnGoingPane() {
-        Conference conf = mConversation.getCurrentCall();
+        Conference conf = mConversation == null ? null : mConversation.getCurrentCall();
         if (conf != null) {
             getView().goToCallActivity(conf.getId());
         } else {