fix: if no previous prod release, return 1.0.0 if no prerelease

[stdavis]

Here's an example of what this fixes: agrc/plpco-rdcc-notifications#147

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 73.11%. Comparing base (1b90386) to head (7665d34).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/utils.ts	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #184      +/-   ##
==========================================
+ Coverage   72.52%   73.11%   +0.59%     
==========================================
  Files           4        4              
  Lines         182      186       +4     
  Branches       30       32       +2     
==========================================
+ Hits          132      136       +4     
  Misses         48       48              
  Partials        2        2              

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