unblockClient: avoid to reset client when the client was shutdown-blocked (#10440)

fix #10439. see https://github.com/redis/redis/pull/9872
When executing SHUTDOWN we pause the client so we can un-pause it
if the shutdown fails.
this could happen during the timeout, if the shutdown is aborted, but could
also happen from withing the initial `call()` to shutdown, if the rdb save fails.
in that case when we return to `call()`, we'll crash if `c->cmd` has been set to NULL.

The call stack is:
```
unblockClient(c)
replyToClientsBlockedOnShutdown()
cancelShutdown()
finishShutdown()
prepareForShutdown()
shutdownCommand()
```

what's special about SHUTDOWN in that respect is that it can be paused,
and then un-paused before the original `call()` returns.
tests where added for both failed shutdown, and a followup successful one.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/blocked.c b/src/blocked.c
index a982884c4..2754da9e0 100644
--- a/src/blocked.c
+++ b/src/blocked.c
@@ -204,7 +204,7 @@ void unblockClient(client *c) {
      * we do not do it immediately after the command returns (when the
      * client got blocked) in order to be still able to access the argument
      * vector from module callbacks and updateStatsOnUnblock. */
-    if (c->btype != BLOCKED_POSTPONE) {
+    if (c->btype != BLOCKED_POSTPONE && c->btype != BLOCKED_SHUTDOWN) {
         freeClientOriginalArgv(c);
         resetClient(c);
     }