Bug 969609 - [B2G][Email]Opening an email notification then pressing back in the email app leads to a black screen.

Manual v1.3 branch merge from master commit 2a439c1dd68b9336b7b0ff14df9b742943aa61bf
Merge pull request #18493 from jrburke/bug969609-v1.3-email-notification-black-screen

Bug 969609 - [B2G][Email]Opening an email notification then pressing back in the email app leads to a black screen. r=asuth a=bajaj