fix hsetex handling of wrong number of fields (valkey-io#2509)

currently hsetex is verifying the number of fields matches the provided
number of fields by using div. instead it can match to the
multiplication in order to prevent rounding the verified value down.

---------

Signed-off-by: Ran Shidlansik <ranshid@amazon.com>
Co-authored-by: Madelyn Olson <madelyneolson@gmail.com>

Author: ranshid

src/t_hash.c

@@ -1200,7 +1200,7 @@ void hsetexCommand(client *c) {
         }
     }
     /* Check that the parsed fields number matches the real provided number of fields */
-    if (!num_fields || num_fields != (c->argc - fields_index) / 2) {
+    if (!num_fields || num_fields > LLONG_MAX / 2 || (num_fields * 2) != (c->argc - fields_index)) {
         addReplyError(c, "numfields should be greater than 0 and match the provided number of fields");
         return;
     }

tests/unit/hashexpire.tcl

@@ -623,10 +623,9 @@ start_server {tags {"hashexpire"}} {
         set e
     } {ERR *}
 
-    # test {HSETEX PX - mismatched field/value count} {
-    #     catch {r HSETEX myhash PX 100 FIELDS 2 field1 val1} e
-    #     set e
-    # } {ERR wrong number of arguments for 'hsetex' command}
+    test {HSETEX PX - mismatched field/value count} {
+         assert_error {ERR numfields should be greater than 0 and match the provided number of fields} {r HSETEX myhash PX 100 FIELDS 1 field1 val1 extra}
+    } 
 
 
     ## FNX/FXX