You could ask Kovid if that would be a reasonable change to make, but for the moment there is no way.
You could try opening a command prompt and typing
Code:
calibredb list -s 'authors:"=J. K. Rowling" '
This would actually be the fastest way I could think of checking an author.
You could even put it into a batch file, say, foo.bat, like such:
Code:
@echo off
calibredb list -s 'authors:"=%*"'
then use Ctrl+R to get a run prompt and
Code:
foo.bat J. K. Rowling
to get all the books you have by J. K. Rowling.