builds/unix/ftsystem.c prevents to open an useless stream from
zero-sized file and returns FT_Err_Cannot_Open_Stream, but the
stream drivers for ANSI C, Amiga and VMS return useless streams.
For cross-platform consistency, all stream drivers should act
same.
* src/base/ftsystem.c (FT_Stream_Open): If the size of the opened
file is zero, FT_Err_Cannot_Open_Stream is returned.
* builds/amiga/src/base/ftsystem.c (FT_Stream_Open): Ditto.
* src/vms/ftsystem.c (FT_Stream_Open): Ditto.
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