Update sh_createitems.lua

Added an IsValid check when entities are spawned. Previously, the error 'attempt to index field 'dt' (a nil value)' was shown, which has got me (and others) stuck a few times.
Merge pull request #1488 from vrondakis/patch-2

Update sh_createitems.lua
Very minor optimisations
Fixed typo in hook name
Merge branch 'master' of github.com:FPtje/DarkRP
Removed pretty much dead code. Small optimisation
Minor optimisations
Optimisation with Lockdowns.

Seriously, GetConVarNumber is god damn slow
Optimised agenda drawing
Optimisation in drawing localplayer info
Optimisation in player info drawing
Merge branch 'master' into workshop