videodb: SQL query fixes for clean database

These are two SQL query fixes I came across while looking into an improved database clean logic.
* The first commit adds missing handling for NULLed fields because otherwise those paths aren't deleted even though they don't exist anymore.
* The second commit removes the condition on strHash. I don't see why we would want to keep around a non-existing path just because we already calculated its fast hash?

I'm not 100% sure about the second commit which is why I made this a PR.