fix(Core/Groups): pass actual loot count to OnPlayerGroupRollRewardItem hook

[myfmwei]

Summary

• OnPlayerGroupRollRewardItem was passing _item->GetCount() as the count parameter, which returns the total stack size after merging into the player's
  existing inventory
• Changed to item->count (LootItem::count) which correctly represents the number of items actually looted from the roll
• Affects both NEED and GREED roll paths in Group.cpp

Problem

If a player had 3 of a stackable item in their bag and won 2 more via a group roll, the script hook would receive count = 5 (merged stack total) instead of
count = 2 (items actually awarded). The PLAYER_EVENT_ON_LOOT_ITEM hook already used LootItem::count correctly — this fix makes the roll reward hook
consistent with it.

Test plan

• Player wins a stackable item via NEED roll while already having some in inventory — verify script hook receives the looted count, not the total stack count
• Player wins a stackable item via GREED roll — same verification
• Player wins a non-stackable item — count should be 1 in both before and after

[sogladev]

Thank you for fixing this