patch 9.2.0343: tests: test_clientserver may fail on slower systems

patch 9.2.0343: tests: test_clientserver may fail on slower systems

Problem:  tests: test_clientserver may fail on slower systems
Solution: Wait for argc() before checking argv() (James McCoy).

On slower systems, the argv() check may run before the server has
populated the arg list.

Add a wait for argc() to be 3 to be more tolerant of such systems

closes: #19974

Signed-off-by: James McCoy <jamessan@jamessan.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>