Testbots Crash on msxml3:schema after recent LIBXML2 udpate

After ThFabba,s recent LIBXML2 update the regression test for msxml3:schema has been constantly crashing. Here is the update for reference:

https://github.com/reactos/reactos/commit/40ee59d609a4597e904888a2242e318aba6cab81

I have created a patch that synchronizes this test to Wine-6.14 and adds protections around the code that causes the crashes so that the test will run again. There were four lines of existing code that did not protect against NULL pointers. I plan to create a PR for this soon. Here is the patch:  winetest_msxml3_schema_c.patch