display: Correctly add minor axis to snapping

There was an issue where the "minor" axis snapping would not be done if
the "major" axis snapping had a zero distance. This could be seen when e.g.
moving a monitor on the right up/down slightly. In that case, no
snapping to align the bottom/top edges were done unless you also moved
the mouse sideways a bit.

Fixes #211
11 jobs for benzea/arrangement-snapping in 13 minutes and 21 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #116161
build

00:06:54

 
  Test
passed #116163
asan

00:06:25

passed #116162
test

00:00:38

 
  Manual
manual #116168
allowed to fail manual
armv8
manual #116164
allowed to fail manual
flatpak
manual #116167
allowed to fail manual
msan
manual #116169
allowed to fail manual
ppc64le
manual #116165
allowed to fail manual
tsan
manual #116166
allowed to fail manual
ubsan
 
  Review
manual #116170
allowed to fail manual
review
manual #116171
allowed to fail manual
stop_review