argv mem leak during multi command execution. (#9598)

Changes in #9528 lead to memory leak if the command implementation
used rewriteClientCommandArgument inside MULTI-EXEC.

Adding an explicit test for that case since the test that uncovered it
didn't specifically target this scenario

src/multi.c

@@ -159,7 +159,7 @@ void execCommandAbort(client *c, sds error) {
 void execCommand(client *c) {
     int j;
     robj **orig_argv;
-    int orig_argc;
+    int orig_argc, orig_argv_len;
     struct redisCommand *orig_cmd;
     int was_master = server.masterhost == NULL;
 
@@ -201,11 +201,12 @@ void execCommand(client *c) {
     server.in_exec = 1;
 
     orig_argv = c->argv;
+    orig_argv_len = c->argv_len;
     orig_argc = c->argc;
     orig_cmd = c->cmd;
     addReplyArrayLen(c,c->mstate.count);
     for (j = 0; j < c->mstate.count; j++) {
-        c->argc = c->mstate.commands[j].argc;
+        c->argv_len = c->argc = c->mstate.commands[j].argc;
         c->argv = c->mstate.commands[j].argv;
         c->cmd = c->mstate.commands[j].cmd;
 
@@ -252,6 +253,7 @@ void execCommand(client *c) {
         c->flags &= ~CLIENT_DENY_BLOCKING;
 
     c->argv = orig_argv;
+    c->argv_len = orig_argv_len;
     c->argc = orig_argc;
     c->cmd = orig_cmd;
     discardTransaction(c);

tests/unit/protocol.tcl

@@ -203,6 +203,23 @@ start_server {tags {"protocol network"}} {
         r mset {*}$args
         assert_equal [r get "{k}2"] v2
     }
+    
+    test "test argument rewriting - issue 9598" {
+        # INCRBYFLOAT uses argument rewriting for correct float value propagation.
+        # We use it to make sure argument rewriting works properly. It's important 
+        # this test is run under valgrind to verify there are no memory leaks in 
+        # arg buffer handling.
+        r flushdb
+
+        # Test normal argument handling
+        r set k 0
+        assert_equal [r incrbyfloat k 1.0] 1
+        
+        # Test argument handing in multi-state buffers
+        r multi
+        r incrbyfloat k 1.0
+        assert_equal [r exec] 2
+    }
 
 }