icontheme: correctly fallback to symbolic icons
icontheme: correctly fallback to symbolic icons

When an icon is requested as symbolic, our generic fallback algorithm
uses fullcolor icons when the specified icon name is not found, treating
the "-symbolic" suffix as another component of the icon name.

Change the algorithm to check beforehand if the icon is symbolic, remove
the suffix if so, and re-add it at the end for all the generated icon
names.

https://bugzilla.gnome.org/show_bug.cgi?id=680926

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