jobwait(): fix race if job exits before waiting on it

Problem:  If a job exits while waiting on another job, the on_exit
          handler is queued but f_jobwait() skips it.
Solution: Always do process_wait(), so that handlers are run during
          f_jobwait().

fix #8302

Test case:
    $ BUSTED_ARGS="--repeat=2000 --no-keep-going" TEST_FILE=test/functional/core/job_spec.lua TEST_FILTER=waiting make functionaltest

Failure example (macOS CI):
    FAILED  test/functional/core/job_spec.lua: jobs jobwait will run callbacks while waiting
    test/functional/core/job_spec.lua:606: Expected objects to be the same.
    Passed in:
    (table: 0x1be77c80) {
      [1] = 'notification'
      [2] = 'wait'
     *[3] = {
       *[1] = 3 } }
    Expected:
    (table: 0x1be77d10) {
      [1] = 'notification'
      [2] = 'wait'
     *[3] = {
       *[1] = 4 } }
    stack traceback:
      test/functional/core/job_spec.lua:606: in function <test/functional/core/job_spec.lua:583

1 files changed, 1 insertions, 1 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 683d44a245..89aaab4c4e 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -12487,7 +12487,7 @@ static void f_jobwait(typval_T *argvars, typval_T *rettv, FunPtr fptr)
     }
 
     // if the job already exited, but wasn't freed yet
-    if (jobs[i] == NULL || jobs[i]->stream.proc.status >= 0) {
+    if (jobs[i] == NULL) {
       continue;
     }