Unable to edit in-line if block was empty when created

[brynwhyman]

If a banner block is created from GridFieldDetailForm without any content, when the user attempts to expand the block for in-line editing, the block does not expand. Expected behaviour is the block should expand and allow the user to add content.

Steps to recreate:

1. Add Banner block to page
2. Create Banner block with no content
3. Attempt to expand the block for editing in edit mode
4. Identify that block does not expand

[ScopeyNZ]

Issue moved to silverstripe/silverstripe-elemental-fileblock #7 via ZenHub