Fix some potential out-of-memory crashes.

* src/base/ftobjs.c (ft_glyphslot_done): Check `slot->internal'.
* src/base/ftstream.c (FT_Stream_ReleaseFrame): Check `stream'.
* src/truetype/ttinterp.c (TT_New_Context): Avoid double-free of
`exec' in case of failure.
4 files changed