after scanning a group invite link, message-input-bar is missing

[r10s]

after scanning a group invite link, the handshake runs for a moment.

during this time, the message-input-bar is not shown (as the user cannot sent as eg. the member list and overall state is unknown - scanning the QR code could also be done when being totally offline)

once, handshake is completed (maybe secondds or days later :), the user can type and the message-input-bar should be shown - which is not the case currently, probably after #2114

when leaving and re-entering the chat, message-input-bar is shown