Fix aimEntity bug

[Sandalot]

Previously did not return the world entity as the world is considered an invalid entity.

[Divran]

This will probably break old E2s for not much gain. This function has worked that way for so long, it'd introduce unexpected behavior to change it now.

Also, you can already get the aim entity even if it's the world if you switch to using Ply:eyeTraceNoCursor():entity() instead of Ply:aimEntity() which won't have much, if any, performance impact since they do the same thing under the hood

edit: also it's not a bug

[Sandalot]

Fair enough, didn't know that Ply:eyeTraceNoCursor() was available.