Fix some compiler warnings, one of which was a legit bug.

MSVC warns that not all control paths return a value when a switch
doesn't have a default case handler.  Changed explicit value checks
to a default check.

Also, it caught a case where bitwise AND was being used instead of
logical AND.  I'm not sure what this fixes, but presumably it is
not covered by any kind of test case.

llvm-svn: 221636