parse_remote_port: ignore colons without port number

Obviously, browsers ignore a colon without a following port number. Both
Firefox and Chrome just removes the colon for such URLs. This change
does not remove the colon for URLs sent over a HTTP proxy, so we should
consider doing that change as well.

Reported by: github user 'kreshano'

lib/url.c

@@ -4319,6 +4319,11 @@ static CURLcode parse_remote_port(struct SessionHandle *data,
       *portptr = '\0'; /* cut off the name there */
       conn->remote_port = curlx_ultous(port);
     }
+    else if(!port)
+      /* Browser behavior adaptation. If there's a colon with no digits after,
+         just cut off the name there which makes us ignore the colon and just
+         use the default port. Firefox and Chrome both do that. */
+      *portptr = '\0';
   }
   return CURLE_OK;
 }