manager: Use ternary operator instead of if/else block

Less code is better code.

src/calls-manager.c

@@ -219,15 +219,9 @@ on_message (CallsMessageSource *source,
                                     message);
   }
 
-  if (notification) {
   calls_message_source_emit_message (CALLS_MESSAGE_SOURCE (self),
-                                       notification,
+                                     notification ? : message,
                                      message_type);
-  } else {
-    calls_message_source_emit_message (CALLS_MESSAGE_SOURCE (self),
-                                       message,
-                                       message_type);
-  }
 }