[kcmkwin/rules] Return absolute path of decoration color scheme

Summary:
We need to return the absolute path instead of base name so decoColorToCombo
can return the correct index.

Test Plan:
* Go to System Settings > Window Management > Window Rules;
* Create a new rule for Konsole to force the Oxygen color scheme,
  close the dialog, and click the Apply button;
* Open the rules dialog (you don't have to modify anything), click OK button, then Apply button.

Without this patch, Breeze color scheme will be forced after the
last step.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: graesslin, broulik, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D17655

kcmkwin/kwinrules/ruleswidget.cpp

@@ -629,7 +629,7 @@ Rules* RulesWidget::rules() const
     CHECKBOX_SET_RULE(below,);
     CHECKBOX_SET_RULE(noborder,);
     auto comboToDecocolor = [this](int index) -> QString {
-        return QFileInfo(decocolor->itemData(index).toString()).baseName();
+        return decocolor->itemData(index).toString();
     };
     COMBOBOX_FORCE_RULE(decocolor, comboToDecocolor);
     CHECKBOX_SET_RULE(skiptaskbar,);