Efm perl: few fixed

Trivial fix for uninitialized warning and more complicated fix for checking stdin.

Current version of efm_perl run perl twice to check separately for errors and warnings, and while checking stdin this result in first perl read stdin up to EOF, and second perl unable to check because stdin already at EOF. In most cases stdin will be a pipe, so it's not seek-able, and we've to make it seek-able to be able to feed second perl with same contents.