android: bug fixes

> NPE: ConversationFacade.readMessages called by DRing
> NPE: CallPresenter.switchVideoInputClick

Change-Id: Iec2b8a26dac3635f81051311726a13d9a56d1af5
diff --git a/ring-android/libringclient/src/main/java/cx/ring/call/CallPresenter.java b/ring-android/libringclient/src/main/java/cx/ring/call/CallPresenter.java
index 30c18e2..6c7a612 100644
--- a/ring-android/libringclient/src/main/java/cx/ring/call/CallPresenter.java
+++ b/ring-android/libringclient/src/main/java/cx/ring/call/CallPresenter.java
@@ -222,6 +222,9 @@
     }
 
     public void switchVideoInputClick() {
+        if(mSipCall == null)
+            return;
+
         mHardwareService.switchInput(mSipCall.getCallId(), false);
         getView().switchCameraIcon(mHardwareService.isPreviewFromFrontCamera());
     }
diff --git a/ring-android/libringclient/src/main/java/cx/ring/facades/ConversationFacade.java b/ring-android/libringclient/src/main/java/cx/ring/facades/ConversationFacade.java
index 12c73f6..c563759 100644
--- a/ring-android/libringclient/src/main/java/cx/ring/facades/ConversationFacade.java
+++ b/ring-android/libringclient/src/main/java/cx/ring/facades/ConversationFacade.java
@@ -156,7 +156,8 @@
 
     public void readMessages(String accountId, Uri contact) {
         Account account = mAccountService.getAccount(accountId);
-        readMessages(account, account.getByUri(contact));
+        if(account != null)
+            readMessages(account, account.getByUri(contact));
     }
 
     public void readMessages(Account account, Conversation conversation) {