* src/truetype/ttvarc.c (tt_varc_get_axis_indices): Fix zeros decoding.

A TupleValues "zeros" run decodes to zero values, matching HarfBuzz
(`TupleValues::decompile`, which memsets the run to 0) and fontTools; the
code instead wrote the running index (`indices[i] = i`), so a zeros run of
length two or more overrode the wrong axes.  No test font exercises it (they
use runs of length one, where 0 == i).

Also bound the run reads by the entry's own `tuple_limit` rather than the
whole-table `table_limit`, so a run straddling the entry end no longer
decodes bytes from adjacent entries (matches the counting pass in
`tt_varc_parse_component`).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>