Multiple issues with `sub_6FC6A8C0`

[Necrolis]

sub_6FC6A8C0 (the function that spawns offset minions for tentacles) contains multiple issues.

1. D2MOO/source/D2Game/src/MONSTER/MonsterSpawn.cpp

   Line 1484 in 8322494

   D2CoordStrc stru_6FD28B68[12] =

   
   This array should be static constexpr or at least static const.

2. D2MOO/source/D2Game/src/MONSTER/MonsterSpawn.cpp

   Line 1521 in 8322494

   const int32_t nIndex = 2 * (nParam1 + nParam2);

   
   The calculated index is incorrect and will lead to OOB reads ((5 + 6) * 2 == 22). the original code does not multiply by 2, it simply adds the two values and then indexes (which is a multiply by 8 (sizeof(D2PositionStrc)) in the assembly).

3. D2MOO/source/D2Game/src/MONSTER/MonsterSpawn.cpp

   Line 1523 in 8322494

   D2UnkMonCreateStrc monCreate = {};

   
   The initialization of monCreate not only has a redundant default initializer, but should also be hoisted out the loop, only the x & y positions change.

4. D2MOO/source/D2Game/src/MONSTER/MonsterSpawn.cpp

   Line 1506 in 8322494

   if (a6 < 0 || a6 > 2)

   
   This line contains a vanilla bug: if a6 == 2 then we have OOB reads (and stru_6FD28B68 is indeed only 12 elements as its followed directly by the ancients monequip array in 1.13). a6 should be bounded to [0, 1] (it can also be renamed to bNonWaterSpawn since the only call site for this function passes in a value by checking the water spawning monster creation flag and then inverts it, aka !(Flags & 4); though it was likely done as an integral value so the raised code is closer to (~(flags >> 2)) & 1.