Fixes SegFault w/ flashlights & attached power

[TRScheel]

Summary

Bugfixes "Fixes SegFault w/ flashlights & attached power"

Purpose of change

There was a segfault occuring on

Cataclysm-DDA/src/item.cpp

Line 12277 in de687d3

const ammotype &loaded_ammo = ammo_data()->ammo->type;

when turning on a heavy-duty flashlight while it is simultaneously connected to a power source (ie. a vehicle) and does not have a battery. See #78580

Describe the solution

Added:

• a short circuit check for ammo to address this issue in the future in
  case there are any other edge cases where this occurs.
• a check for a linked power source so the light source uses the
  power source's linked power when determining the illumination value.

Describe alternatives you've considered

I didn't consider any other alternatives.

Testing

I loaded CDDA in a dev environment prior to this fix and created a test world and saved it once I had the conditions necessary to reproduce the bug. In that test world, I then turned on the flashlight and successfully reproduced the bug.

After applying the fix, I loaded the same save and attempted the same action. This time successfully due to the fix. In addition, I spawned a normal vehicle, attached the flashlight to it, and ensured there was a power draw occurring (there was). Then I removed the battery while the flashlight was on to ensure that it both turned off (it did) and that the game did not crash (it did not).

Additional context

I used

Cataclysm-DDA/src/item.cpp

Line 14177 in de687d3

if( !has_link_data() || link().charge_rate == 0 || link().charge_interval < 1 ) {

as a reference for the linked power check above. This means the two power checks are extremely similar and it makes me believe that it would be beneficial to have a function such as has_link_power that returns a boolean (true for has power, false otherwise). My only hesitation is that I do not know where else that sort of power check is done and what the complete scope of the checks against charge_rate / charge_interval are for.