Fixed warning on CWriteFile

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@5382 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/CWriteFile.cpp

@@ -111,7 +111,7 @@ bool CWriteFile::flush()
 	if (!isOpen())
 		return false;
 
-	return !(bool) fflush(File);
+	return fflush(File) == 0; // 0 indicates success, otherwise EOF and errno is set
 }
 
 IWriteFile* CWriteFile::createWriteFile(const io::path& fileName, bool append)