age-plugin: Fix no-label recipient plugins with old clients

[str4d]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 51.14%. Comparing base (bdec23f) to head (e8f1444).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
age-plugin/src/recipient.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #542      +/-   ##
==========================================
+ Coverage   51.06%   51.14%   +0.07%     
==========================================
  Files          43       43              
  Lines        4159     4159              
==========================================
+ Hits         2124     2127       +3     
+ Misses       2035     2032       -3     

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