Empty markdown lists are not idempotent and eventually collapse to incorrect output.

Prettier 1.11.1

Step 1:

When there are spaces after period, they are removed
Playground link

Input:

1. 
2. 
3. 
4. 

Output:

1.
2.
3.
4.

Rendered: (this is fine)
1.
2.
3.
4.

Step 2:

When there are no spaces after period, list collapses
Playground link

Input:

1.
2.
3.
4.

Output:

1. 2. 3. 4.

Rendered: (not okay)

Step 3:

In a collapsed list, single space becomes double space
Playground link

Input:

1. 2. 3. 4.

Output:

1.  2.  3.  4.

Expected behavior:

1. Running prettier on the same file three times should not result in three different outputs.
2. Prettier should not change the meaning of the markdown