Weekly Bugzilla Report mail: Fix wrong SQL query on bug resolutions

No, this query really didn't do what it was supposed to. The new one
at least works fine in my local MySQL shell, but testing it again
with the PHP script on the server wouldn't be a bad idea.

Bug: 48072
Change-Id: If088ab6a7ebc26e793f5fb3991d4446a0c5e05f2