Description:

Fixes a red screen that would come up when trying to paste plain text at the end of a block or when text was selected.

Dependencies:

Gutenberg PR: WordPress/gutenberg#14011

Known issues:

The text selection after pasting is not correct, but this is not a problem introduced by this PR.

Testing:

Test 1:

1. Copy some plain text.
2. Select some text from a block.
3. Paste

Make sure you don't get a red screen.

Test 2:

1. Copy some plain text.
2. Place the caret at the end of a paragraph or heading block.
3. Paste

Make sure you don't get a red screen.