* process.c: Add sanity checks for file descriptors.

* process.c: Add sanity checks for file descriptors.

(wait_reading_process_output, Fprocess_filter_multibyte_p):
Check that infd is nonnegative before using it as an fd.
(read_and_dispose_of_process_output, Fprocess_send_eof):
Likewise, for outfd.
(wait_reading_process_output): Omit unnecessary check of infd.

Fixes: debbugs:17844