Cache results of GUIObject::isConditionTrue()

Signed-off-by: Vojtech Bocek <vbocek@gmail.com>

Change-Id: Ia50f7c365b2dc0a65ee046bb42972e3594264878
diff --git a/gui/fileselector.cpp b/gui/fileselector.cpp
index 484bcff..e1570ed 100644
--- a/gui/fileselector.cpp
+++ b/gui/fileselector.cpp
@@ -865,8 +865,10 @@
 	return 0;
 }
 
-int GUIFileSelector::NotifyVarChange(std::string varName, std::string value)
+int GUIFileSelector::NotifyVarChange(const std::string& varName, const std::string& value)
 {
+	GUIObject::NotifyVarChange(varName, value);
+
 	if(!isConditionTrue())
 		return 0;