Fix autogen exclude for comments under package

[hypnoglow]

The commit df4f676 broke the exclusion of autogenerated files that have appropriate comments below the package statement.

Some tools put DO NOT EDIT comment not in the beginning of the file but below the package statement, for example minimock: https://github.com/gojuno/minimock/blob/master/tests/formatter_mock.go

For such autogenerated files detection stopped working since the commit mentioned above.

This commit fixes the issue by allow scanning below the package statement.

[CLAassistant]

All committers have signed the CLA.

[jirfag]

thank you for this fix!