A previous commit tried to eliminate a panic when reading an empty
profile by stopping support for profiles with no samples. That is
unnecessary and it can obstruct some testing.

The panic was caused by the legacy parser returning a nil profile and
no error when processing an empty profile. Detect that situation and
generate a proper profile instead.

Tested by running 'pprof /dev/null'
Add testcase for profile parsing errors

- Remove dead code, unnecessary conversions
- Consistently use a single space after period

Also update the build instructions to use go get