[bdf] Fix Savannah bug #41692.

bdflib puts data from the input stream into a buffer in chunks of
1024 bytes.  The data itself gets then parsed line by line, simply
increasing the current pointer into the buffer; if the search for
the final newline character exceeds the buffer size, more data gets
read.

However, in case the current line's end is very near to the buffer
end, and the keyword to compare with is longer than the current
line's length, an out-of-bounds read might happen since `memcmp'
doesn't stop properly at the string end.

* src/bdf/bdflib.c: s/ft_memcmp/ft_strncmp/ to make comparisons
stop at string ends.
[cff] Fix Savannah bug #41693.

* src/cff/cffload.c (CFF_Load_FD_Select): Reject empty array.
[winfnt] Fix Savannah bug #41694.

* src/winfonts/winfnt.c (FNT_Load_Glyph): Check glyph offset.