Fix null-response NPE in outgoing MMS

Fixes #2839
Closes #2840

// FREEBIE

src/org/thoughtcrime/securesms/mms/OutgoingLegacyMmsConnection.java

@@ -20,6 +20,7 @@ import android.content.Context;
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 import android.net.Uri;
+import android.support.annotation.NonNull;
 import android.util.Log;
 
 import org.apache.http.Header;
@@ -70,7 +71,7 @@ public class OutgoingLegacyMmsConnection extends LegacyMmsConnection implements
   }
 
   @Override
-  public SendConf send(byte[] pduBytes) throws UndeliverableMessageException {
+  public SendConf send(@NonNull byte[] pduBytes) throws UndeliverableMessageException {
     try {
       MmsRadio radio = MmsRadio.getInstance(context);
 

src/org/thoughtcrime/securesms/mms/OutgoingLollipopMmsConnection.java

@@ -21,6 +21,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.os.Build.VERSION;
 import android.os.Build.VERSION_CODES;
+import android.support.annotation.NonNull;
 import android.telephony.SmsManager;
 import android.util.Log;
 
@@ -57,7 +58,7 @@ public class OutgoingLollipopMmsConnection extends LollipopMmsConnection impleme
 
   @Override
   @TargetApi(VERSION_CODES.LOLLIPOP)
-  public synchronized SendConf send(byte[] pduBytes) throws UndeliverableMessageException {
+  public synchronized SendConf send(@NonNull byte[] pduBytes) throws UndeliverableMessageException {
     beginTransaction();
     try {
       MmsBodyProvider.Pointer pointer = MmsBodyProvider.makeTemporaryPointer(getContext());
@@ -74,6 +75,10 @@ public class OutgoingLollipopMmsConnection extends LollipopMmsConnection impleme
       Log.w(TAG, "MMS broadcast received and processed.");
       pointer.close();
 
+      if (response == null) {
+        throw new UndeliverableMessageException("Null response.");
+      }
+
       return (SendConf) new PduParser(response).parse();
     } catch (IOException | TimeoutException e) {
       throw new UndeliverableMessageException(e);

src/org/thoughtcrime/securesms/mms/OutgoingMmsConnection.java

@@ -1,9 +1,11 @@
 package org.thoughtcrime.securesms.mms;
 
+import android.support.annotation.NonNull;
+
 import org.thoughtcrime.securesms.transport.UndeliverableMessageException;
 
 import ws.com.google.android.mms.pdu.SendConf;
 
 public interface OutgoingMmsConnection {
-  SendConf send(byte[] pduBytes) throws UndeliverableMessageException;
+  SendConf send(@NonNull byte[] pduBytes) throws UndeliverableMessageException;
 }