fix(ui): show date divider for first message

[imtoori]

fixes #842

[codecov]

Codecov Report

Merging #1090 (d70b2e5) into develop (8bdcc6b) will decrease coverage by 0.01%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##           develop    #1090      +/-   ##
===========================================
- Coverage    76.12%   76.10%   -0.02%     
===========================================
  Files          193      193              
  Lines        20693    20699       +6     
===========================================
+ Hits         15753    15754       +1     
- Misses        4940     4945       +5     

Impacted Files	Coverage Δ
...stream_chat_flutter/lib/src/message_list_view.dart	46.30% <66.66%> (-0.36%)	⬇️

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