[psaux, type1] Fix minor AFM issues.

* include/internal/t1types.h (AFM_KernPairRec): Make indices
unsigned.
Update users.
(AFM_FontInfoRec): Make element counters unsigned.
Update users.
* src/psaux/afmparse.h (AFM_ValueRec): Add union member for unsigned
int.

* src/psaux/afmparse.c (afm_parse_track_kern, afm_parse_kern_pairs):
Reject negative values for number of kerning elements.

* src/type1/t1afm.c, src/tools/test_afm.c: Updated.
6 files changed