Fix a 'garbage value' warning found by Clang's static analyzer

This commit fixes #167

 - Initialize lists in paragraph_start()
 - Remove two dead stores

I reviewed all warnings/errors generated by Clang's static analyzer on Xcode. Many `NULL dereference` bugs are not worth removing as they are virtually impossible to reproduce as they happen inside deeply nested blocks inside really long functions.

The dead stores are not worth removing as many of them actually make sense. Most them are preventive resets of variables (e.g. some_list = NULL, len = 0).

I found the cases I've fixed worth fixing. `fmt_check_par()` is called inside `paragraph_start()` and checks whether `???_flags` are `NULL` or `???_len` are `0`.