Fix uninitialized variable

echo | awk 'BEGIN {i=$1; print i}' prints a boatload of stack
garbage. NUL terminate the memory returned from malloc to prevent it.

Obtained from: OpenBSD run.c 1.40
Sponsored by: Netflix

Fix %c for floating values that become 0 when coerced to int.

Obtained from: OpenBSD run.c 1.36 (From Jeremy Devenport)
Sponsored by: Netflix, Inc

Don't display empty error context.

Context extraction didn't handle this case and showed uninitialized memory.

Obtained from: OpenBSD lib.c 1.21
Sponsored by: Netflix