Handling the ActivityCanceled event from Gecko in SMS application when Home button is pressed to avaoid application error

Removed else statement as per the review comments
Merge pull request #11140 from leob2g/Bug_896958_ShowingWrongErrorMessage_WhenOpeningSMSapp_AfterHomeButton_isPressed

[MMS][896958]Handling the ActivityCanceled event from Gecko in SMS application when Home button is pressed to avaoid application error. r=borjasalguero