[0.14.5] Crash with damage_interval=0 on beam

[Lilly]

Creating a beam entity with damage_interval=0 causes factorio to crash with a SIGSEGV.

Steps to reproduce:
1. Install the attached 'lines' mod. This mod creates a beam entity upon 'on_player_created'. The beam has damage_interval=0.
2. Start factorio.
3. Start a new game.
4. Factorio crashes with a SIGSEGV on tick 0 (always).

Workaround:
Set damage_interval of the beam in 'lines_0.0.1/data.lua' to something else, like 1000. In this case the game won't crash. (Though, the rendering of the beam seems to be incorrect.)

[Rseding91]

Fixed for 0.14.6. It now can't be 0. 1 will cause the beam attack to be applied each tick.