preview bug when deleting one line before a header

[shisaru292]

Description

When deleting content before a header including the \n char, the preview of the header becomes common text but number signs(#) of the header are still regraded as special signs(which are hidden).

• Can you reproduce the issue?

Steps to reproduce

see gif of actual behavior.

Expected behavior:

Considering the actual markdown text, the header shouldn't change its look.

Actual behavior:

Versions

• Mark Text version: v0.16.3
• Operating system: Win10