Use unsigned long for maxiterations, fixing undefined behavior in scan with extremely large count

src/db.c

@@ -1199,7 +1199,7 @@ void scanGenericCommand(client *c, robj *o, unsigned long long cursor) {
          * COUNT, so if the hash table is in a pathological state (very
          * sparsely populated) we avoid to block too much time at the cost
          * of returning no or very few elements. */
-        long maxiterations = count * 10;
+        unsigned long maxiterations = (unsigned long)count * 10UL;
 
         /* We pass scanData which have three pointers to the callback:
          * 1. data.keys: the list to which it will add new elements;