pypi: handle ignore_non_pypi_packages correctly

Signed-off-by: William Woodruff <william@yossarian.net>

Library/Homebrew/utils/pypi.rb

@@ -235,6 +235,7 @@ module PyPI
       if main_package.valid_pypi_package?
         main_package.version = version
       else
+        return if ignore_non_pypi_packages
         odie "The main package is not a PyPI package. Please update its URL manually."
       end
     end