settings: ensure we don't call isProtectedApp with an invalid reference

isProtectedApp could be called from onPrepareOptionsMenu with an invalid mPackageInfo
reference. Just ensure the activity doesn't crash by return false (with an invalid
mPackageInfo reference the acitivty will be closed).

Change-Id: Ifa4754decefce726e6703d38744f6c5b7878437f
JIRA: NIGHTLIES-1949
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>