eliminate 'goto's in dbcheck.cpp and musicdbcheck.cpp

[ulmus-scott]

Checklist

• [x] contribution does not duplicate one of our existing pull requests
• [x] contribution is in a branch rebased against master
• [x] code compiles successfully without errors
• [x] code follows the MythTV Coding Standards
• [x] documentation added/updated/removed where necessary
• [x] commits are logically organised and have good commit messages