Merge pull request #15993 from jaoo/934916

Bug 934916 - [WAP push][CP] If a CP message is opened, newly coming CP or WAP push messages can still be opened but content is not displayed. r=gsvelto(cherry picked from commit 3ad11b1058a0ec4e9a64d7a786e7863b7bff27e5)

Conflicts:
	apps/wappush/test/unit/wappush_test.js