[Crash] Can cause a crash if you accept a group invite, and sent a raid invite previously that was then accepted.

[Aeadoin]

Steps to reproduce:

1. Invite Player 2 to raid.
2. Send group invite from Player 2 to Player 1.
3. Accept group invite on Player 1.
4. Accept raid invite on Player 2.
5. Results in EXCEPTION_ACCESS_VIOLATION in client_packet.cpp

Code where crash occurs:

if (group->members[x]) {
if (!client_to_add) {
if (group->members[x]->IsClient()) {

Most likely some sort of dangling pointer to group still exists, resulting in a crash when we try to deference group->members[x]->IsClient()