Fix: Moving the last page item to the the trash causes a crash.

[jorgefilipecosta]

Fixes an issue found by @jasmussen, where when there is only a single page available on the all-pages view. Moving the page to the trash crashes the application.

Testing Instructions

Go to the site editor -> pages.
On the all pages view move all the pages to the trash so there is only a single page left.
Now move that single page to the trash and verify everything worked well on trunk a crash happens.

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Co-authored-by: jorgefilipecosta <jorgefilipecosta@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>
Co-authored-by: jasmussen <joen@git.wordpress.org>

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[jasmussen]

Nice, thanks for working on this.

[Mamaduka]

Thank you, @jorgefilipecosta!

The fix works as expected, and it makes sense to add this check.