fix a fopen bug: rb should be w
diff --git a/tinyxml2.cpp b/tinyxml2.cpp
index c7f19b9..0bee8bf 100644
--- a/tinyxml2.cpp
+++ b/tinyxml2.cpp
@@ -1602,7 +1602,7 @@
 		errno_t err = fopen_s(&fp, filename, "w" );

 		if ( !fp || err) {

 	#else

-		fp = fopen( filename, "rb" );

+		fp = fopen( filename, "w" );

 		if ( !fp) {

 	#endif

 		SetError( XML_ERROR_FILE_COULD_NOT_BE_OPENED, filename, 0 );