Set _isMounted to true after component mounted

[janus-reith]

Signed-off-by: Janus Reith mail@janusreith.de

Resolves #699
Impact: minor
Type: bugfix

Issue

In 0ae583e#diff-9b6019bce1be1df5431a56f4a139663dL77 I removed the whole componentDidMount part, not realizing that this._isMounted = true; was unrelated to the tracking events underneath.

Solution

Add back a componentDidMount lifecycle function to set _isMounted to true in the first place.
Don't close #699 until confirmed that there is no separate issue present on older versions, where the component might actually not be mounted properly.

Testing

See #699

[manueldelreal]

functionally it seems to be ok, I was able to checkout, and get an error message when using stripe and when disallowing guest checkout (to avoid IOU from completing)

[willopez]

LGTM

[willopez]

Thanks @janus-reith!