fix #1279: mediautils crash
fix #1261
fix cacheDir initialization
Merge pull request #1282 from wordpress-mobile/issue/1279-npe-mediautils

fix #1279 and #1261 - 2.7.3 crashes
Merge branch 'master' into develop
Merge branch 'develop' of https://github.com/wordpress-mobile/WordPress-Android into feature/reader-blog-detail