body_length_limit collapses blank lines in commit body #2079

Description

When body_length_limit is enabled, blank lines in the commit body are removed.

Reproduction

With body_length_limit = 80 (or cz commit --body-length-limit 80), create a commit message like:

feat: subject

First paragraph line

Second paragraph line

Expected behavior

Blank lines in the body are preserved, and only long non-empty lines are wrapped.

Actual behavior

The blank line between the two body paragraphs is removed:

feat: subject

First paragraph line
Second paragraph line