GetNewDrop() allocated newdrop up front but returned NULL without
freeing it on every rejection path (failed drop-rate check, missing
drop table, unknown item type, etc.), leaking on every non-drop roll.
Free it on all early-return paths, and only assign a clientid once a
drop is actually going to be returned.
CPacket::AddByte/Word/DWord/QWord/Float now bounds-check against the
buffer before writing, preventing an overflow if a packet is built
past its allocated size.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
