Add more warnings to W3

[sweemer]

These two warnings are not enabled by default at the W3 level, but they are nice to have in the CI so I have added them.

[coveralls]

coverage: 72.642%. remained the same
when pulling 638cbf2 on sweemer:more-w3
into 0e83ab7 on lballabio:master.

[lballabio]

Agreed that they're nice to have in the CI, but we might think about adding them in the CI builds and not as defaults. I'm thinking of the people that might be modifying the sources, or adding to them; we might be triggering warnings in their code that they might not want to deal with right now. It's probably not a lot of people, though.

[lballabio]

I think the right fix is to remove this early return and leave the extra check below.

[sweemer]

Fixed

[sweemer]

Agreed that they're nice to have in the CI, but we might think about adding them in the CI builds and not as defaults. I'm thinking of the people that might be modifying the sources, or adding to them; we might be triggering warnings in their code that they might not want to deal with right now. It's probably not a lot of people, though.

As far as I understand, the CI warnings should all be enabled when QL_ENABLE_DEFAULT_WARNING_LEVEL is on, in order to ensure consistency with the CI. People who turn this option off will only see compiler warnings enabled, which is the W1 level for MSVC. So adding this warning to the W3 level should not affect those users.