Core/Spells: Fixed crashes happening with spells that had their dbc targets overriden

Closes #10395
Scripts/OnyxiasLair: Fix a crash in boss_onyxia

Closes #10393

Note: this just fixes the crash, not the issues the script has (a.k.a rewrite this)
DB/Spells: Fix some startup errors
Revert "CMake/MSVC: Fix VS 2013 compile -- Zm500 hack is no longer required"

This reverts commit ca7377369f603081259adea0ba49cb03e74e609f.
Merge remote-tracking branch 'origin/master' into 4.3.4

Conflicts:
	src/server/game/Spells/SpellInfo.cpp
	src/server/game/Spells/SpellMgr.cpp
Core/Spells: Fix a merge error
Merge branch '4.3.4' of https://github.com/TrinityCore/TrinityCore