xargs: terminate if line replacement cannot be constructed

If the line with replacement cannot be constructed xargs should
terminate as documented in the man page

We encounter this error, but gnu/xargs doesn't because they have a much
larger limit for created outputs (~10000 lines).

Reviewed by: oshogbo
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D35574