Coverity fixes

Contains 4 fixes:
- Devision by zero is on the 'tot' variable in ws.cc. Technically if the statring is empty, the value would be 0 and you devide by zero. Now we just check and stop if there's no stats. I'm not sure if that's correct and i'm not sure if coverity will understand that this makes sure we always have tot > 0 like this.
- d_tid was not initialized in the constructor of the webserver. We now set it to 0, which should fix the coverity error.

- d_minimum was not initialized in the constructor of mydnsbackend.cc.
- The parent pointer was never used in the mydnsbackend