gno precompile output parsing can panic

[tbruyelle]

In the gno repo, gno precompile . outputs many things that aren't properly ignored/parsed by gnols.

First of all, the commands reads hidden directories, which shouldn't be avoided, as outlined in gnolang/gno#1381.

Secondly, any parse error are interpreted as if the file has the *.gen.go extension, while it's not necessarily the case.