gtkthemingengine: Eliminate a dead assignment
gtkthemingengine: Eliminate a dead assignment

This is technically a dead assignment, but is nice to retain for
clarity. Moving it to the variable definition shuts scan-build up.

https://bugzilla.gnome.org/show_bug.cgi?id=712760

alexlarsson/gtk,jessevdk/gtk,jadahl/gtk,jadahl/gtk,davidgumberg/gtk,grubersjoe/adwaita,ahodesuka/gtk,davidgumberg/gtk,chergert/gtk,Lyude/gtk-,alexlarsson/gtk,grubersjoe/adwaita,msteinert/gtk,ahodesuka/gtk,chergert/gtk,ahodesuka/gtk,Adamovskiy/gtk,alexlarsson/gtk,Lyude/gtk-,jigpu/gtk,jigpu/gtk,Adamovskiy/gtk,davidgumberg/gtk,Adamovskiy/gtk,jigpu/gtk,grubersjoe/adwaita,jadahl/gtk,ahodesuka/gtk,alexlarsson/gtk,davidgumberg/gtk,ahodesuka/gtk,Lyude/gtk-,jessevdk/gtk,jigpu/gtk,jessevdk/gtk,msteinert/gtk,grubersjoe/adwaita,jessevdk/gtk,grubersjoe/adwaita,alexlarsson/gtk,alexlarsson/gtk,Sidnioulz/SandboxGtk,Adamovskiy/gtk,jigpu/gtk,davidgumberg/gtk,ahodesuka/gtk,chergert/gtk,chergert/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,grubersjoe/adwaita,jigpu/gtk,chergert/gtk,Lyude/gtk-,jadahl/gtk,chergert/gtk,jessevdk/gtk,Adamovskiy/gtk,Lyude/gtk-,jessevdk/gtk,jigpu/gtk,msteinert/gtk,Sidnioulz/SandboxGtk,jadahl/gtk,msteinert/gtk,Adamovskiy/gtk,ahodesuka/gtk,Adamovskiy/gtk,alexlarsson/gtk,ahodesuka/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,jadahl/gtk,msteinert/gtk,Sidnioulz/SandboxGtk,chergert/gtk,grubersjoe/adwaita,grubersjoe/adwaita,msteinert/gtk,jigpu/gtk,jadahl/gtk,davidgumberg/gtk,Adamovskiy/gtk,Lyude/gtk-,davidgumberg/gtk,chergert/gtk,alexlarsson/gtk,jessevdk/gtk,Sidnioulz/SandboxGtk,jadahl/gtk