[CIS-1148] Fix crash on channel delete event

[nuno-vieira]

Description of the pull request

In a channel delete event, we try to parse the createdBy relationship of the ChannelDTO, but it doesn't exist, so it crashes. ChatChannel.createdBy was already optional, so there are no changes required in the customer's code.

Fixes: #1404

[codecov-commenter]

Codecov Report

Merging #1408 (69fb6e7) into main (02574da) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1408      +/-   ##
==========================================
+ Coverage   90.71%   90.77%   +0.06%     
==========================================
  Files         224      224              
  Lines        9873     9873              
==========================================
+ Hits         8956     8962       +6     
+ Misses        917      911       -6     

Flag	Coverage Δ
llc-tests	90.77% <100.00%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
Sources/StreamChat/Database/DTOs/ChannelDTO.swift	93.99% <100.00%> (ø)
...eamChat/APIClient/Endpoints/Payloads/RawJSON.swift	87.17% <0.00%> (-12.83%)	⬇️
.../ChannelListController/ChannelListController.swift	91.33% <0.00%> (+8.66%)	⬆️

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[evsaev]

👍