fix(ui): fix MessageInput to use with non-initialized channel

[xsahil03x]

Description of the pull request

Fixed StreamMessageInput exception: Updated the StreamMessageInput widget to handle cases where the Channel is not initialized. This change introduces a conditional logic using a switch statement to ensure the widget behaves correctly even when channel.state is null. (packages/stream_chat_flutter/lib/src/message_input/stream_message_input.dart)

[Brazol]

LGTM

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 63.21%. Comparing base (fa3d0af) to head (ee4c4eb).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...er/lib/src/message_input/stream_message_input.dart	83.33%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2258   +/-   ##
=======================================
  Coverage   63.21%   63.21%           
=======================================
  Files         402      402           
  Lines       25224    25224           
=======================================
  Hits        15945    15945           
  Misses       9279     9279           

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