This PR fixes #415 by making sure there is at least one Textual block in the list, before applying the hack about the keyboard hiding in the alpha release.

Steps to repro:

• Start the demo app
• Tap on a para block
• Tap on the page break block
• The block holder is selected, but the soft keyboard is still up, and the caret blinking in the previous para block
• If you tap on the keyboard characters are inserted in the para block

Important test

• Start the demo app with empty content
• Tap on '+' symbol and add a page break
• Tap on the page break block and see there is no error

Repeat the steps above by selecting other kind of blocks