extra check in cry() for NULL context

mongoose.c

@@ -584,7 +584,7 @@ static void cry(struct mg_connection *conn, const char *fmt, ...) {
   // same way string option can.
   conn->log_message = buf;
   if (call_user(conn, MG_EVENT_LOG) == NULL) {
-    fp = conn->ctx->config[ERROR_LOG_FILE] == NULL ? NULL :
+    fp = conn->ctx == NULL || conn->ctx->config[ERROR_LOG_FILE] == NULL ? NULL :
       mg_fopen(conn->ctx->config[ERROR_LOG_FILE], "a+");
 
     if (fp != NULL) {