Make geometryRestore() pure virtual in AbstractClient

Provides an implementation in ShellClient and method in Client gets
marked as override.

abstract_client.h

@@ -301,6 +301,7 @@ public:
     virtual TabGroup *tabGroup() const;
     Q_INVOKABLE virtual bool untab(const QRect &toGeometry = QRect(), bool clientRemoved = false);
     virtual bool isCurrentTab() const;
+    virtual QRect geometryRestore() const = 0;
     virtual MaximizeMode maximizeMode() const = 0;
     virtual void maximize(MaximizeMode) = 0;
     virtual bool noBorder() const = 0;

client.h

@@ -239,7 +239,7 @@ public:
     bool isShadeable() const override;
 
     bool isMaximizable() const override;
-    QRect geometryRestore() const;
+    QRect geometryRestore() const override;
     MaximizeMode maximizeMode() const override;
 
     QuickTileMode quickTileMode() const;

shell_client.h

@@ -74,6 +74,9 @@ public:
     void hideClient(bool hide) override;
     void maximize(MaximizeMode) override;
     MaximizeMode maximizeMode() const override;
+    QRect geometryRestore() const override {
+        return m_geomMaximizeRestore;
+    }
     bool noBorder() const override;
     const WindowRules *rules() const override;
     void sendToScreen(int screen) override;