MINIFICPP-1357 - Fix proxy port reading of InvokeHTTP

Signed-off-by: Arpad Boda <aboda@apache.org>

This closes #899
diff --git a/extensions/http-curl/processors/InvokeHTTP.cpp b/extensions/http-curl/processors/InvokeHTTP.cpp
index 4dc4744..5a6dc6b 100644
--- a/extensions/http-curl/processors/InvokeHTTP.cpp
+++ b/extensions/http-curl/processors/InvokeHTTP.cpp
@@ -251,7 +251,10 @@
 
   proxy_ = {};
   context->getProperty(ProxyHost.getName(), proxy_.host);
-  context->getProperty(ProxyPort.getName(), proxy_.port);
+  std::string port_str;
+  if (context->getProperty(ProxyPort.getName(), port_str) && !port_str.empty()) {
+    core::Property::StringToInt(port_str, proxy_.port);
+  }
   context->getProperty(ProxyUsername.getName(), proxy_.username);
   context->getProperty(ProxyPassword.getName(), proxy_.password);
 }