Fix set with duplicate elements causes sdiff to hang (#11530)

This payload produces a set with duplicate elements (listpack encoding):
```
restore _key 0 "\x14\x25\x25\x00\x00\x00\x0A\x00\x06\x01\x82\x5F\x35\x03\x04\x01\x82\x5F\x31\x03\x82\x5F\x33\x03\x00\x01\x82\x5F\x39\x03\x82\x5F\x33\x03\x08\x01\x02\x01\xFF\x0B\x00\x31\xBE\x7D\x41\x01\x03\x5B\xEC"

smembers key
1) "6"
2) "_5"
3) "4"
4) "_1"
5) "_3"  ---> dup
6) "0"
7) "_9"
8) "_3"  ---> dup
9) "8"
10) "2"
```

This kind of sets will cause SDIFF to hang, SDIFF generated a broken
protocol and left the client hung. (Expected ten elements, but only
got nine elements due to the duplication.)

If we set `sanitize-dump-payload` to yes, we will be able to find
the duplicate elements and report "ERR Bad data format".

Discovered and discussed in #11290.

This PR also improve prints when corrupt-dump-fuzzer hangs, it will
print the cmds and the payload, an example like:
```
Testing integration/corrupt-dump-fuzzer
[TIMEOUT]: clients state report follows.
sock6 => (SPAWNED SERVER) pid:28884
Killing still running Redis server 28884
commands caused test to hang:
SDIFF __key 
payload that caused test to hang: "\x14\balabala"
```

Co-authored-by: Oran Agra <oran@redislabs.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/src/t_set.c b/src/t_set.c
index 8ab602791..b56b38238 100644
--- a/src/t_set.c
+++ b/src/t_set.c
@@ -1493,8 +1493,7 @@ void sunionDiffGenericCommand(client *c, robj **setkeys, int setnum,
             }
             if (j == setnum) {
                 /* There is no other set with this element. Add it. */
-                setTypeAddAux(dstset, str, len, llval, encoding == OBJ_ENCODING_HT);
-                cardinality++;
+                cardinality += setTypeAddAux(dstset, str, len, llval, encoding == OBJ_ENCODING_HT);
             }
         }
         setTypeReleaseIterator(si);