Fixes https://github.com/vector-im/riot-web/issues/4311
The cancel button onClick was hooked directly up to onFinished, so
the mouse event ended up as the boolean for whether an email had
been set.
Fixes https://github.com/vector-im/riot-web/issues/4311
This was due to `BaseDialog` calling `onFinished` with a mouse event instead of `false` (and it was assumed to call with `true/false`, but doesn't)