Verify custom HTTP headers, fix off by one error

platform/javascript/http_client_javascript.cpp

@@ -87,6 +87,11 @@ Error HTTPClientJavaScript::request(Method p_method, const String &p_url, const
 	ERR_FAIL_COND_V(port < 0, ERR_UNCONFIGURED);
 	ERR_FAIL_COND_V(!p_url.begins_with("/"), ERR_INVALID_PARAMETER);
 
+	Error err = verify_headers(p_headers);
+	if (err) {
+		return err;
+	}
+
 	String url = (use_tls ? "https://" : "http://") + host + ":" + itos(port) + p_url;
 	Vector<CharString> keeper;
 	Vector<const char *> c_strings;