libxml2 subproject library is sometimes not installed by meson

Building with VS2019 x86

It seems xml2.dll is missing from the installed location c:\gstreamer\1.0\x86\bin.

It is built and found under build_dir\subprojects\libxml2-2.9.7\xml2.dll

Not having the file makes gstbash not work.

Manually putting it in c:\gstreamer\1.0\x86\bin\ resolves the problem.