Page data form inputs should not render until page data exists

Reviewed the code and tested manually, including switching between 0.x and the MR's branch to see the effects, and the problem is gone.

All set.

Left one question on the MR, if I'm wrong feel free to remark as fixed

@larowlan, I think we should move the pageDataExists check inside as it's more specific to page data forms.
I will update the MR with this change. Please confirm if this approach looks good.

Marking as fixed based on @bnjmnm's latest comment. I agree with Ben's response - I think perhaps there is confusion because there is more than one than one React component in this file.