fix: do not recreate the toolbar when the selection is not null

[asjqkkkk]

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.25%. Comparing base (d5c9f64) to head (c855879).

Files with missing lines	Patch %	Lines
...b/src/editor/toolbar/desktop/floating_toolbar.dart	88.88%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1087   +/-   ##
=======================================
  Coverage   71.24%   71.25%           
=======================================
  Files         325      325           
  Lines       15756    15757    +1     
=======================================
+ Hits        11226    11227    +1     
  Misses       4530     4530           

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