Fix glib cmake script and only call OnOpen callback if set

Find glibconfig.h cmake script should use pkgconfig information instead of a hard coded path to /usr/lib. There may be a better way to handle this, but I found on my 64-bit system with both 32-bit and 64-bit versions of glib installed that the wrong version(32-bit) of glibconfig.h was being used and causing a compile error.


the OnOpen callback should be called when set to avoid a segfault.
I was getting a segfault when trying to use tsmf, so I fixed that case here. It looks like there might be a few other cases where we should make sure that the OnOpen function pointer gets set to NULL as well.