When modules are first loaded by `require` in package.lua, it checks
for a return value with `if res then`. If that check fails, the module
will be cached with the default value `true` at line 109, and that
value is then returned.
That check should be changed to `if res ~= nil then`, because
otherwise a module with a return value of `false` will be cached with
the value `true`.
This also necessitates a corresponding change to the check at line 93,
which is when `package.loaded` is initially checked to see if a package
has been loaded before, as that value could be `false`.
Bug: T362045
Change-Id: Id42e26a922c13971c25ed8654e822dc6fdcb6ca7