Fix for bug #695229 - open document from byte array doesn't work, but saving to file and open from file works

Patch was supplied by gong_su@hotmail.com. Thanks!
Prevent the creation/destruction of the fz_cookies from trampling the env/clazz pointers in globals.

The env/clazz pointers are stashed in the globals structure so that they can
be accessed by callback functions in mupdf.c (such as bufferStreamSeek()).

The intention is that only one thread (i.e. the AsyncTask background thread)
reads/writes these stashed pointers. Because cookies are created/destroyed
in the main thread, we add a new version of get_globals() which doesn't trample
these pointers.