room_history: re-enable kinetic scrolling after loading more

Previously kinetic scrolling was disabled while loading more
messages and was never re-enabled. This could lead to rooms
not scrolling with touch gestures.

Now after we add widgets to the top, we re-enable kinetic
scrolling for our ScrolledWindow.

Fixes GNOME/fractal#458
4 jobs for <span class="ref-name">wip/christopherdavis/fix-touch-scrolling</span> in 25 minutes and 52 seconds (queued for 1 second)
Status Job ID Name Coverage
  Check
passed #245315
check

00:00:24

 
  Test
passed #245316
flatpak

00:24:19

 
  Review
passed #245317
review

00:00:44

failed #245318
allowed to fail manual
stop_review

00:00:23

 
Name Stage Failure
failed
stop_review Review
Using Docker executor with image fedora:29 ...
Pulling docker image fedora:29 ...
Using docker image sha256:d09302f77cfcc3e867829d80ff47f9e7738ffef69730d54ec44341a9fb1d359b for fedora:29 ...
Running on runner-d836cf30-project-164-concurrent-0 via gcc150.bak.milne.osuosl.org...
Cloning repository...
Cloning into '/builds/BrainBlasted/fractal'...
Checking out 908a837b as wip/christopherdavis/fix-touch-scrolling...
fatal: reference is not a tree: 908a837b780db3344aa6355e15b933e1113d6f07
ERROR: Job failed: exit code 1