fix #2023: mGridAdapter was called before creation
Merge pull request #2025 from wordpress-mobile/issue/2023-mediagallerypicker-crash

fix #2023: mGridAdapter was called before creation
Merge branch 'release/3.4' into release/3.5
Merge branch 'release/3.5' of github.com:wordpress-mobile/WordPress-Android into release/3.5