http_negotiate: Added empty decoded challenge message info text

lib/http_negotiate.c

@@ -101,8 +101,11 @@ CURLcode Curl_input_negotiate(struct connectdata *conn, bool proxy,
     if(result)
       return result;
 
-    if(!rawlen)
+    if(!rawlen) {
+      infof(data, "Negotiate handshake failure (empty challenge message)\n");
+
       return CURLE_BAD_CONTENT_ENCODING;
+    }
 
     input_token.length = rawlen;
 

lib/http_negotiate_sspi.c

@@ -168,8 +168,12 @@ CURLcode Curl_input_negotiate(struct connectdata *conn, bool proxy,
     if(result)
       return result;
 
-    if(!input_token_len)
+    if(!input_token_len) {
+      infof(conn->data,
+            "Negotiate handshake failure (empty challenge message)\n");
+
       return CURLE_BAD_CONTENT_ENCODING;
+    }
   }
 
   /* Setup the "output" security buffer */