Fix bug in desktop where first track gets stuck loading

[garrettjstevens]

Fixes #2818

This copies rpc.worker.ts from web to desktop. They had diverged a bit in form, but were still doing the same thing, so this hopefully makes them easier to maintain. #2818 was caused by #2798 incorrectly applying the the same change to both these files.

[codecov]

Codecov Report

Merging #2819 (3066d1b) into main (c72cea5) will increase coverage by 0.00%.
The diff coverage is 10.00%.

@@           Coverage Diff           @@
##             main    #2819   +/-   ##
=======================================
  Coverage   59.98%   59.98%           
=======================================
  Files         584      584           
  Lines       26690    26689    -1     
  Branches     6463     6462    -1     
=======================================
  Hits        16010    16010           
+ Misses      10350    10349    -1     
  Partials      330      330           

Impacted Files	Coverage Δ
products/jbrowse-desktop/src/rpc.worker.ts	26.82% <10.00%> (+0.63%)	⬆️

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[cmdcolin]

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