Fix error in 'call-process-region' when START is nil (Bug#40576)

* src/callproc.c (Fcall_process_region): Fix behavior when START is
nil and DELETE is non-nil.

* test/src/callproc-tests.el
(call-process-region-entire-buffer-with-delete): New unit test.
1 job for master in 90 minutes and 1 second (queued for 3 seconds)
Status Job ID Name Coverage
failed #5515


Name Stage Failure
test-all Test The script exceeded the maximum execution time set for the job
make -C test check-expensive
make[1]: Entering directory '/builds/emacs/emacs/test'
rm -f ./*.tmp
make[2]: Entering directory '/builds/emacs/emacs/test'
make[3]: Entering directory '/builds/emacs/emacs/test'
ELC lisp/net/tramp-tests.elc
GEN lisp/net/tramp-tests.log
Pulling docker image gitlab/gitlab-runner-helper:x86_64-d0b76032 ...
ERROR: Job failed: execution took longer than 1h30m0s seconds