+ character in a fragmented list does not work correctly

[devkev]

Describe the bug
If I have a fragmented list entry where the text of the line contains a + character, then the list item does not render correctly.

Samples to Reproduce

In all of the below cases, the list entries render correctly if the + is changed to -.

Example 1:

- foo
+ a + b

renders as:

- foo
- a - b

Example 2:

- foo
+ `a + b`

renders as

- foo
- a - &shy;<!-- .element: class="fragment" -->b

Example 3:

- foo
+ c = a + b

renders as

- foo
- c="true" =="true" a - b

Expected behavior
Fragmented list entries should always render identically to the corresponding non-fragmented list entry.

I believe that the problem is (or is related to) the list fragment replacement code erroneously considering all "+ " sub-strings in a line, when in fact it should only consider those at the start of the line or preceeded only by whitespace, ie. those matching a regex of "^\s*+". (h/t @rueckstiess for finding the problematic code)

[MSzturc]

will be fixed with upcoming version