Deleting Heading Block content requires extra backspace to show placeholder

[mchowning]

Describe the bug
On Android only, when deleting the text in a heading, deleting the last character does not reveal the placeholder text. Instead, you have to press an additional backspace (when the heading appears to be empty) for the Heading's placeholder text to appear.

To Reproduce
Steps to reproduce the behavior:

1. Create a Heading block containing a single character
2. Press backspace
3. Observe the heading is empty and that there is no placeholder text
4. Press backspace
5. Observe the placeholder text appears

Expected behavior

Deleting the last character in a heading should immediately reveal the placeholder text

Smartphone

Pixel, Android 10, gutenberg-mobile 7644a01

[mchowning]

Seems like there is a good chance this may have the same underlying cause as #1524