Fix for contrived NPE on invalid recipient during conversation compose.

res/values/strings.xml

@@ -81,6 +81,7 @@
     <string name="ConversationActivity_group_conversation">Group Conversation</string>
     <string name="ConversationActivity_d_recipients_in_group">%d recipients in group</string>    
     <string name="ConversationActivity_saving_draft">Saving draft...</string>
+    <string name="ConversationActivity_invalid_recipient">Invalid recipient!</string>
     
     <!-- ConversationFragment -->
     <string name="ConversationFragment_message_details">Message details</string>

src/org/thoughtcrime/securesms/ConversationActivity.java

@@ -300,6 +300,12 @@ public class ConversationActivity extends PassphraseRequiredSherlockFragmentActi
   }
 
   private void handleStartSecureSession() {
+    if (getRecipients() == null) {
+      Toast.makeText(this, getString(R.string.ConversationActivity_invalid_recipient),
+                     Toast.LENGTH_LONG).show();
+      return;
+    }
+
     final Recipient recipient   = getRecipients().getPrimaryRecipient();
     String recipientName        = (recipient.getName() == null ? recipient.getNumber() : recipient.getName());
     AlertDialog.Builder builder = new AlertDialog.Builder(this);