Fix disabled state on the linear genome view track labels dropdown menu

[cmdcolin]

Currently the track menu can be disabled in embedded mode if there are no "items" but there should always be at least an "About track" dialog

[codecov]

Codecov Report

Merging #2695 (e50ea88) into main (b7184e1) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2695      +/-   ##
==========================================
- Coverage   60.71%   60.71%   -0.01%     
==========================================
  Files         561      561              
  Lines       26350    26350              
  Branches     6425     6425              
==========================================
- Hits        15999    15998       -1     
- Misses      10025    10026       +1     
  Partials      326      326              

Impacted Files	Coverage Δ
...iew/src/LinearGenomeView/components/TrackLabel.tsx	97.05% <100.00%> (ø)
...ckages/core/pluggableElementTypes/RpcMethodType.ts	83.33% <0.00%> (-2.09%)	⬇️
products/jbrowse-web/src/util.ts	27.27% <0.00%> (ø)

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