Increment delivery counter on XCLAIM unless RETRYCOUNT specified

The XCLAIM docs state the XCLAIM increments the delivery counter for
messages. This PR makes the code match the documentation - which seems
like the desired behaviour - whilst still allowing RETRYCOUNT to be
specified manually.

My understanding of the way streamPropagateXCLAIM() works is that this
change will safely propagate to replicas since retry count is pulled
directly from the streamNACK struct.

Fixes #5194

src/t_stream.c

@@ -2279,8 +2279,12 @@ void xclaimCommand(client *c) {
             /* Update the consumer and idle time. */
             nack->consumer = consumer;
             nack->delivery_time = deliverytime;
-            /* Set the delivery attempts counter if given. */
+            /* Set the delivery attempts counter if given, otherwise autoincrement */
-            if (retrycount >= 0) nack->delivery_count = retrycount;
+            if (retrycount >= 0) {
+                nack->delivery_count = retrycount;
+            } else {
+                nack->delivery_count++;
+            }
             /* Add the entry in the new consumer local PEL. */
             raxInsert(consumer->pel,buf,sizeof(buf),nack,NULL);
             /* Send the reply for this entry. */

tests/unit/type/stream-cgroups.tcl

@@ -195,6 +195,35 @@ start_server {
         assert_equal "" [lindex $reply 0]
     }
 
+    test {XCLAIM increments delivery count} {
+        # Add 3 items into the stream, and create a consumer group
+        r del mystream
+        set id1 [r XADD mystream * a 1]
+        set id2 [r XADD mystream * b 2]
+        set id3 [r XADD mystream * c 3]
+        r XGROUP CREATE mystream mygroup 0
+
+        # Client 1 reads item 1 from the stream without acknowledgements.
+        # Client 2 then claims pending item 1 from the PEL of client 1
+        set reply [
+            r XREADGROUP GROUP mygroup client1 count 1 STREAMS mystream >
+        ]
+        assert {[llength [lindex $reply 0 1 0 1]] == 2}
+        assert {[lindex $reply 0 1 0 1] eq {a 1}}
+        r debug sleep 0.2
+        set reply [
+            r XCLAIM mystream mygroup client2 10 $id1
+        ]
+        assert {[llength [lindex $reply 0 1]] == 2}
+        assert {[lindex $reply 0 1] eq {a 1}}
+
+        set reply [
+            r XPENDING mystream mygroup - + 10
+        ]
+        assert {[llength [lindex $reply 0]] == 4}
+        assert {[lindex $reply 0 3] == 2}
+    }
+
     start_server {} {
         set master [srv -1 client]
         set master_host [srv -1 host]