[stream] Fix reading s32 when long is s64

`FT_READ_LONG`, `FT_GET_LONG`, and related macros did not return
negative values when `long` is more than 32 bits. `FT_Stream_ReadULong`
would read four bytes into the LSB of an `FT_ULong` and return that.
Since this can never set the MSb of the `FT_ULong` when `FT_ULong` is
more than 32 bits the cast to `FT_Long` never resulted in a negative

Fix this by modifying `FT_Stream_Read*` to return a type of the same
size as the bytes it is reading and changing the `FT_READ_*` and
`FT_GET_*` macros to cast to the same type returned by `FT_Stream_Read*`
but with the correctly signed type (instead of casting to what is
assumed to be the type of `var` which will happen automatically anyway).

There exist a few cases like with the `OFF3` variants where there isn't
generally a type with the correct size. `FT_PEEK_OFF3` works around this
loading the bytes into the three most significant bits and then doing a
signed shift down. `FT_NEXT_OFF3` also already worked correctly by
casting this signed value to another signed type. `FT_Stream_GetUOffset`
works correctly but one must be careful not to attempt to cast the
returned value to a signed type. Fortunately there is only
`FT_GET_UOFF3` and no `FT_GET_OFF3`.

All of these cases are handled correctly when reading values through
`FT_Stream_ReadFields` since it generically computes the signed value
through an `FT_Int32`. This change is essentially doing the same for
these macros.

* include/freetype/internal/ftstream.h (FT_NEXT_*, FT_GET_*, FT_READ*):
Update macros and return types to use fixed size types for fixed size

* src/base/ftstream.c (FT_StreamGet*, FT_StreamRead*): Dito.

Issue: #1161
2 files changed