Ensure that our variable checking for >= 0 is signed

Ensure that our variable checking for >= 0 is signed

Last-Update: 2020-03-17
Bug-Debian: https://bugs.debian.org/954127

The type of v->n is size_t, which is an unsigned type, and we are assigning
v->n - 1 to i and looping while this is >= 0.  If v->n == 0, on some
architectures (armhf) this results in i being set to a positive value
(specifically, UINT32_MAX).

Gbp-Pq: Name ensure-signed-comparison.patch