libdraw: replace hand-rolled realloc, preventing buffer overflow. The original buffer is f->nsubf*sizeof *subf bytes (oldsize) large. Once it's full, a new buffer of (f->nsubf+DSUBF)*sizeof *subf (newsize) is mallocated. Unfortunately memmove() reads (newsize) bytes from the original (oldsize) buffer, causing a buffer overflow. By switching to realloc(), we don't need to do buffer size calculation, memmoving, and freeing of the original buffer. Change-Id: Ibf85bc06abe1c8275b11acb1d7d346a14291d2cd Reviewed-on: https://plan9port-review.googlesource.com/1520 Reviewed-by: Gleydson Soares <gsoares@gmail.com>

more places where display can be nil

handle arbitrary length names in subfontname. handle overflow in offset computation in font.c

make it possible to access fonts without a display.

Amazingly picky bug fixes from Valgrind.

Initial revision