fix: Custom Scp127 clipsizes causing desyncs

[Someone-193]

Description

Describe the changes
I fixed a small nullability issue then changed the methods directly using base game SetAmmo methods to use Exileds methods (which check the AmmoType to be valid)

What is the current behavior? (You can also link to an open issue here)
Scp 127's AmmoType is 255 for exiled cuz NW never added an official ammo for 127. Because of this, when a Custom Weapon 127 reloads and calls OnInternalReloaded, it would do ev.Player.Inventory.ServerSetAmmo(args); and cause the client to desync because the use AmmoType was None

What is the new behavior? (if this is a feature change)

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

Other information:
Why didn't Ttrouble just use ev.Player.SetAmmo 😭

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentations

Submission checklist

• I have checked the project can be compiled
• I have tested my changes and it worked as expected

Patches (if there are any changes related to Harmony patches)

• I have checked no IL patching errors in the console

Other

• Still requires more testing