fix: Calculate premask from BOLD when sbref is provided

[effigies]

Paired with nipreps/niworkflows#1001, attempt to fix nipreps/niworkflows#1000.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 72.90%. Comparing base (e0a5aeb) to head (1c8b499). :warning: Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3574      +/-   ##
==========================================
+ Coverage   72.88%   72.90%   +0.01%     
==========================================
  Files          60       60              
  Lines        4821     4824       +3     
  Branches      626      627       +1     
==========================================
+ Hits         3514     3517       +3     
  Misses       1164     1164              
  Partials      143      143              

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