Avoid divide by zero in vehicle::print_fuel_indicator

[pjf]

Summary

None

Purpose of change

Stop crash to desktop on examining some vehicles.

Fixes #64407.

Describe the solution

Checked if the fuel cap for a given fuel was zero, and avoided showing/calculating time-to-full/empty calculations if it is.

Describe alternatives you've considered

None.

Testing

Loaded save in #64407 without patch applied. Game crashes on vehicle examination.

Loaded save in #64407 with patch applied. Vehicle can be examined fine.

Additional context

None.

[irwiss]

I can't reproduce the crash using the save from linked PR on commit b738ae2
I think the actual repro case happened on a weirdly generated wreck and failed to survive a save/load cycle
Likely it's caused by something I changed in #64097 though

I think it might be worth it to do the cap == 0 case handling earlier; since with verbose == true and debug_mode == false the division by 0 will happen on line 437

[pjf]

@irwiss : Well heck, I've now tried it with the save as well and can't reproduce it either. A weird wreck that didn't survive a save/load cycle makes perfect sense, especially since weird wrecks have been the bane of my existence.

Adding more comments in #64407.

[irwiss]

I mean regardless of reproduction it's probably a good idea to block division by zero, but your solution misses the case you described in the issue:
When examining vehicle the function is called with verbose=true, and unless you're in debug mode you'll divide at line 437 before you get to the check you added

[pjf]

When examining vehicle the function is called with verbose=true, and unless you're in debug mode you'll divide at line 437 before you get to the check you added

Oh gosh, you're absolutely right. PR updated.