0052-ps/output.c: Handle negative snprintf() return value.

0052-ps/output.c: Handle negative snprintf() return value.

May happen if strlen(src) > INT_MAX for example. This patch prevents
escaped_copy() from increasing maxroom and returning -1 (= number of
bytes consumed in dst).

---------------------------- adapted for newlib branch
. formerly applied to proc/escape.c
. function was moved to ps/output.c

Signed-off-by: Jim Warner <james.warner@comcast.net>