This was originally added as a workaround for a Mesa bug by commit
ddf52dda. The other half of the hack has since
been removed. This code causes problems when wglDeleteContext() from a
different thread causes our current context to be destroyed, since
wglGetCurrentContext() will return a destroyed context in that case. That is a
flaw in our wgl implementation, since wglDeleteContext() shouldn't allow a
context that's current in a different thread to be destroyed, but this hack is
a bad idea regardless.