Handle small python/bash scripts

Hi Simon,

This is a minor fix for handling coverage of small python/bash scripts.  The peek_file() method returns NULL for files smaller than 512 bytes, so no coverage is generated.

Test bash and python scripts are included; prior to this fix, running kcov on either script would exit returning 1.  With the fix, coverage (100%) is generated for each script.

Regards,
    Chris