If memory allocations fail at certain points while opening a font,
FreeType can either crash due to a NULL dereference or leak memory.
* include/freetype/internal/ftobjs.c (FT_Face_InternalRec,
FT_LibraryRec): Make `refcount' a signed integer. If, for example,
FT_Open_Face() fails in a memory allocation before the face's
reference count is set to 1, a subsequent `FT_Done_Library' call
would otherwise loop over `FT_Done_Face' 2^32 times before freeing
the face.
* src/base/ftobjs.c (open_face): Initialize `stream' and friends
earlier.
(FT_Open_Face) <Fail>: Behave correctly if `node' is NULL.
(FT_Destroy_Module) <Fail>: Check that `renderer_clazz' is valid.
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