glib: Fix use of uninitialized members in PopplerInputStream

https://bugs.freedesktop.org/show_bug.cgi?id=82630
Fix rendering of file with a wrong embedded font

Bug #84270
0.26.5
Cairo backend added to Qt4 wrapper
Setting default Qt4 backend to Cairo
Forcing subpixel rendering in Cairo backend
Enabling slight hinting in Cairo Backend

Originally suggested at:
http://bugs.freedesktop.org/show_bug.cgi?id=3307#c20