Fix error on accessing encrypted media without keys
Fix error on accessing encrypted media without keys

In case where the message is encrypted and you request cross-signed keys
from another session you may end up in a situation where `media` doesn't
exist as you didn't receive keys, yet you have the message's type.
This commit fixes this problem by checking if the media is even available.

matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk