Fix using numeric cheats with a non-numeric value.
Requested by @Silier at r26328 / rP26328.
This notifies players when using a non-numeric value and guards the simulation against such cases.
Previous behaviour was that a cheat was executed with its default value. Now the cheat is not used.
Differential revision: https://code.wildfiregames.com/D4485
Comments by: @bb, @Silier