Eliminate repeated virtual calls

tinyxml2.cpp

@@ -913,7 +913,8 @@ XMLNode* XMLText::ShallowClone( XMLDocument* doc ) const
 
 bool XMLText::ShallowEqual( const XMLNode* compare ) const
 {
-    return ( compare->ToText() && XMLUtil::StringEqual( compare->ToText()->Value(), Value() ));
+    const XMLText* text = compare->ToText();
+    return ( text && XMLUtil::StringEqual( text->Value(), Value() ) );
 }