fix: slot 'none' is number 0, not number -1

[midgleyc]

Off #1510, likely cause of autoscend issues.

Can confirm the issue (an issue) is fixed by running ash equipped_item($slot[none]) and not getting an error.

[codecov]

Codecov Report

Merging #1536 (85f0e81) into main (d8c40bc) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1536      +/-   ##
============================================
- Coverage     34.98%   34.97%   -0.02%     
+ Complexity    17588    17584       -4     
============================================
  Files          1067     1067              
  Lines        163603   163603              
  Branches      34947    34947              
============================================
- Hits          57234    57212      -22     
- Misses        96823    96848      +25     
+ Partials       9546     9543       -3     

Impacted Files	Coverage Δ
src/net/sourceforge/kolmafia/textui/DataTypes.java	52.19% <100.00%> (ø)
...net/sourceforge/kolmafia/textui/DataFileCache.java	37.73% <0.00%> (-5.67%)	⬇️
.../sourceforge/kolmafia/request/StandardRequest.java	81.08% <0.00%> (-2.71%)	⬇️
.../sourceforge/kolmafia/preferences/Preferences.java	84.84% <0.00%> (-1.59%)	⬇️
...forge/kolmafia/textui/langserver/FilesMonitor.java	79.48% <0.00%> (-1.29%)	⬇️
...lmafia/swingui/widget/ListCellRendererFactory.java	29.10% <0.00%> (-0.47%)	⬇️
...net/sourceforge/kolmafia/swingui/GenericFrame.java	23.91% <0.00%> (-0.28%)	⬇️
src/net/sourceforge/kolmafia/KoLCharacter.java	64.26% <0.00%> (-0.13%)	⬇️

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[jaadams5]

I trust your manual tests worked. I can run autoscend tomorrow.