Codechange: Assign/StoreSizePosition x/y can be negative. (#11416)

AssignSizePosition is used with negative values when an NWidgetMatrix is
scrolled, but they were passed as unsigned and then stored as signed.

Widget pos_x/pos_y were already made signed.

src/smallmap_gui.cpp

@@ -1740,7 +1740,7 @@ public:
 		this->resize_y = std::min(display->resize_y, bar->resize_y);
 	}
 
-	void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool rtl) override
+	void AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool rtl) override
 	{
 		this->pos_x = x;
 		this->pos_y = y;