multipress: Only emit preedit signals if needed
multipress: Only emit preedit signals if needed

When clearing the compose buffer, don't emit preedit-changed
unconditionally. This triggers a recursion which leads to
a crash.

https://bugzilla.gnome.org/show_bug.cgi?id=753644

jadahl/gtk,davidgumberg/gtk,alexlarsson/gtk,chergert/gtk,jadahl/gtk,jadahl/gtk,jigpu/gtk,alexlarsson/gtk,grubersjoe/adwaita,chergert/gtk,jadahl/gtk,chergert/gtk,davidgumberg/gtk,chergert/gtk,jadahl/gtk,jigpu/gtk,alexlarsson/gtk,alexlarsson/gtk,jigpu/gtk,davidgumberg/gtk,jigpu/gtk,grubersjoe/adwaita,davidgumberg/gtk,jadahl/gtk,jadahl/gtk,grubersjoe/adwaita,alexlarsson/gtk,jigpu/gtk,grubersjoe/adwaita,chergert/gtk,jigpu/gtk,chergert/gtk,alexlarsson/gtk,alexlarsson/gtk,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jigpu/gtk,alexlarsson/gtk,chergert/gtk,grubersjoe/adwaita,jigpu/gtk,jadahl/gtk,davidgumberg/gtk,grubersjoe/adwaita,davidgumberg/gtk,davidgumberg/gtk