Check if a queue is present. Return an error otherwise

features/cellular/easy_cellular/CellularConnectionFSM.cpp

@@ -136,6 +136,10 @@ nsapi_error_t CellularConnectionFSM::init()
     }
 
     _at_queue = _cellularDevice->get_queue();
+    if (!_at_queue) {
+        stop();
+        return NSAPI_ERROR_NO_MEMORY;
+    }
     _at_queue->chain(&_queue);
 
     _retry_count = 0;