assertion on master when deleting an empty chunk from inside

[Scott Kostyshak]

To reproduce, on master open mwe.lyx, place the cursor inside of the
empty chunk, and press Backspace.

Can others reproduce?

Note also that when I export mwe.lyx to 2.1.x format, the separator is
gone and there is an ERT with whitespace in it. I don't know if this
is incorrect and if so if it is related to the assertion.

Scott

mwe.lyx
Description: application/lyx

mwe.21.lyx
Description: application/lyx