Fix a crash in MigrateThumbnailsDatabase.
Fix a crash in MigrateThumbnailsDatabase.

BUG=53161
TEST=unit_tests

Review URL: http://codereview.chromium.org/3162037

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@57535 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser