Bold and italic toggle doesn't work properly selecting more lines.

**Describe the bug**
-create two rows (second row in a new line)
-put the cursor at the end of second line
-press control A to select all
-press control B to select bold (it correctly select bold)
-press control B again to to toggle bold, but it leaves the last ** delimiter

**Expected behavior**
when I press control B the second time it should remove any bold delimiter

same for italic

Reproduce the issue in the EasyMDE editor using two lines, Ctrl+A, and repeated bold or italic toggles. Trace the selection-formatting behavior for the editor entry point, then verify that toggling off removes all formatting delimiters, including the trailing delimiter.

Written by the indexing model from the issue text.