FIX: fix lang_code for hms

Change-Id: I75035f8d0fe70b35683cc383ca139c0377bf3a14

src/slic3r/GUI/HMS.cpp

@@ -143,6 +143,7 @@ std::string HMSQuery::hms_language_code()
         // set language code to en by default
         return "en";
     }
+    return lang_code;
 }
 
 std::string HMSQuery::get_hms_file()