Fix max_lag stuff

[S-S-X]

Must be fixed if this gets merged luanti-org/luanti#11077
Should be fixed anyway even if above does not get merged.

Not technically bug yet... there was no wanna-be-bug label...

Stuff that must be "fixed" is here:
https://github.com/mt-mods/technic/blob/master/technic/max_lag.lua

[BuckarooBanzay]

possible "fix" is just to return a default value if the parsing fails: #192 (fixes #191 in the short term)

Another fix would be to not rely on that value at all, its used in the radiation-code (to disable the cpu-heavy raycasting operations on high lag) and in the switching-station globalstep (to kinda-dynamically reduce the globalstep work).