Fix crash in "Open session" widget for sessions that have 'track-less views'

[cmdcolin]

some view types, e.g. MsaView, do not have any tracks, and this caused the Open session widget to crash (it tries to calculate sum of all view.tracks)

[codecov]

Codecov Report

Merging #4043 (4b4236c) into main (f12cb41) will decrease coverage by 0.02%.
The diff coverage is 45.83%.

❗ Current head 4b4236c differs from pull request most recent head fba1d65. Consider uploading reports for the commit fba1d65 to get more accurate results

@@            Coverage Diff             @@
##             main    #4043      +/-   ##
==========================================
- Coverage   63.63%   63.62%   -0.02%     
==========================================
  Files        1029     1031       +2     
  Lines       30304    30309       +5     
  Branches     7213     7218       +5     
==========================================
- Hits        19284    19283       -1     
- Misses      10854    10859       +5     
- Partials      166      167       +1     

Files	Coverage Δ
...ionManager/components/DeleteSavedSessionDialog.tsx	0.00% <ø> (ø)
...s/src/SessionManager/components/SessionManager.tsx	100.00% <100.00%> (+61.36%)	⬆️
...browse-web/src/components/SessionWarningDialog.tsx	41.17% <ø> (ø)
...essionManager/components/AutosavedSessionsList.tsx	58.82% <58.82%> (ø)
...ionManager/components/RegularSavedSessionsList.tsx	34.48% <34.48%> (ø)

... and 3 files with indirect coverage changes

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