Preallocate string in CXMLWriter::writeText to speedup xml-writing somewhat.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4175 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/CXMLWriter.cpp

@@ -205,7 +205,8 @@ void CXMLWriter::writeText(const wchar_t* text)
 	if (!File || !text)
 		return;
 
-	core::stringw s;
+	core::stringw s(text);
+	s = L""; // passing text and then resetting it is a (little ackward) way to reserve memory for the string to avoid lots of reallocations below.
 	const wchar_t* p = text;
 
 	while(*p)