Add an error check for empty path of an URL

Author: long-long-float

libraries/HTTPClient/src/HTTPClient.cpp

@@ -261,6 +261,10 @@ bool HTTPClient::beginInternal(String url, const char* expectedProtocol)
     url.remove(0, (index + 3)); // remove http:// or https://
 
     index = url.indexOf('/');
+    if (index == -1) {
+        log_e("the path of url must not be empty");
+        return false;
+    }
     String host = url.substring(0, index);
     url.remove(0, index); // remove host part