Target: correct the return value for `GetImageAddrFromToken`

We would return `LLDB_INVALID_IMAGE_TOKEN` for the address rather than
the correct value of `LLDB_IMAGE_ADDRESS`.  This would result in the
check for the return value to silently pass on x64 as the invalid
address and invalid token are of different sizes (`size_t` vs
`uintprr_t`).  This corrects the return value to `LLDB_INVALID_ADDRESS`
and addresses the rest to reset the mapped address to the invalid value.

This was found by inspection when trying to implement module support for
Windows.