If unsigned int is 32-bits long, then our old code would give a
wrong result with any log domain whose mask was >= (1<<32).
Fortunately, there are no such log domains right now: the domain
mask is only 64 bits long to accommodate some flags.
Found by coverity as CID 1452041.
Fixes bug 31451; bugfix on 0.4.1.4-rc.
