(#3325) - fix blob support w/ duplicate idbs

Just fixing this dumb bug, since my big refactor might not end up working in IE10.

FWIW, in Chrome 39 blobSupport is still false for some reason. Should probably investigate that separately.

Test fails before the fix, succeeds after.
I'm not sure why we had this; it could potentially call `checkSetupComplete()` twice, which is wrong.