Marktext should not add new lines between numbered list items

Description

Marktext adds new lines between numbered list items

• Can you reproduce the issue?

Steps to reproduce

1. Have simple Markdown document with numbered list inside:

   Some text before list:
   
   1. First
   1. Second with subitems
   
      * red
      * orange
      * blue
   
   1. Third
   
   Some text after list.
   

   Including last line it has 13 lines of code and 126 bytes in size.

2. Open this document using MarkText

3. Close MarkText confirming document save

Expected behavior:

the MarkText does not change the document

Actual behavior:

the MarkText changed the document contents and added empty lines between ordered list items:

Some text before list:

1. First

2. Second with subitems
   
   * red
   * orange
   * blue

3. Third

Some text after list.

Note: such document changes add difficulties to version control. The 1., 2. and 3. are already known as https://github.com/marktext/marktext/issues/2035 .

Versions

• Mark Text version: MarkText 0.16.3 (from FlatPak)
• Operating system: Ubuntu MATE 18.04 LTS

Start by reproducing the save cycle with the 13-line Markdown document described in the issue, then compare the original and saved contents to isolate where blank lines are introduced. Trace the document save or Markdown formatting entry point responsible for ordered lists and verify that saving preserves the original list spacing and nested items.