Cache results of GUIObject::isConditionTrue()

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

Change-Id: Ia50f7c365b2dc0a65ee046bb42972e3594264878
diff --git a/gui/text.cpp b/gui/text.cpp
index 715880b..c594f48 100644
--- a/gui/text.cpp
+++ b/gui/text.cpp
@@ -222,8 +222,10 @@
 	}
 }
 
-int GUIText::NotifyVarChange(std::string varName, std::string value)
+int GUIText::NotifyVarChange(const std::string& varName, const std::string& value)
 {
+	GUIObject::NotifyVarChange(varName, value);
+
 	mVarChanged = 1;
 	return 0;
 }