egl/glvnd: Fix a segfault in eglGetProcAddress.

egl/glvnd: Fix a segfault in eglGetProcAddress.

If FindProcIndex in egldispatchstubs.c is called with a name that's less than
the first entry in the array, it would end up trying to store an index of -1 in
an unsigned integer, wrap around to 2^32, and then crash when it tries to look
that up.

Change FindProcIndex so that it uses bsearch(3) instead of implementing its own
binary search, like the GLX equivalent FindGLXFunction does.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>