(sync) ignore non-existent message?

[mistermoe]

@bobbilee19 encountered the following error:

Sync failed due to error:  TypeError: Cannot read properties of undefined (reading 'descriptor')
    at _SyncApi.getDwnMessageType_fn (file:///Users/bobbilee/TBD/web5-app/node_modules/@tbd54566975/web5-user-agent/dist/esm/main.mjs:1072:21)
    at _SyncApi.<anonymous> (file:///Users/bobbilee/TBD/web5-app/node_modules/@tbd54566975/web5-user-agent/dist/esm/main.mjs:886:95)
    at Generator.next (<anonymous>)
    at fulfilled (file:///Users/bobbilee/TBD/web5-app/node_modules/@tbd54566975/web5-user-agent/dist/esm/main.mjs:46:24)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

i don't have a reliable way to reproduce this error, but this PR introduces a best-guess fix that also happens to address a TODO. I'm pretty sure the added check will fix the bug because getDwnMessageType is only called in 1 place

[codecov]

Codecov Report

Merging #114 (49f8e7b) into main (dd83cec) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #114      +/-   ##
==========================================
+ Coverage   65.97%   66.05%   +0.08%     
==========================================
  Files          31       31              
  Lines        3447     3456       +9     
  Branches      195      195              
==========================================
+ Hits         2274     2283       +9     
  Misses       1171     1171              
  Partials        2        2              

Components	Coverage Δ
crypto	0.00% <ø> (ø)
dids	48.61% <ø> (ø)
web5	81.32% <ø> (ø)
web5-agent	0.00% <ø> (ø)
web5-proxy-agent	0.00% <ø> (ø)
web5-user-agent	79.63% <100.00%> (+0.14%)	⬆️

[mistermoe]

published an alpha release that @bobbilee19 pulled into her project and is no longer encountering the errors that she was seeing previously

[mistermoe]

link to relevant part of discord discussion here