Fix: Online Players list mouse hover behaviour.

Hover highlight was visible even if the mouse pointer was in a different
window, and the window refreshed itself every frame if the mouse pointer
was not over its matrix widget.

Resolved by using OnMouseOver() instead of OnMouseLoop(), and only
redrawing if the hover position has changed.

src/network/network_gui.cpp

@@ -2115,21 +2115,19 @@ public:
 		}
 	}
 
-	virtual void OnMouseLoop() override
+	void OnMouseOver(Point pt, int widget) override
 	{
-		if (GetWidgetFromPos(this, _cursor.pos.x - this->left, _cursor.pos.y - this->top) != WID_CL_MATRIX) {
-			this->hover_index = -1;
-			this->SetDirty();
-			return;
-		}
-
-		NWidgetBase *nwi = this->GetWidget<NWidgetBase>(WID_CL_MATRIX);
-		int y = _cursor.pos.y - this->top - nwi->pos_y - 2;
-		int index = y / this->line_height;
-
-		if (index != this->hover_index) {
-			this->hover_index = index;
-			this->SetDirty();
+		if (widget != WID_CL_MATRIX) {
+			if (this->hover_index != -1) {
+				this->hover_index = -1;
+				this->SetWidgetDirty(WID_CL_MATRIX);
+			}
+		} else {
+			int index = this->GetRowFromWidget(pt.y, widget, 0, -1);
+			if (index != this->hover_index) {
+				this->hover_index = index;
+				this->SetWidgetDirty(WID_CL_MATRIX);
+			}
 		}
 	}
 };