SHERLOCK: Fix icon disappearing when moving to Covent Gradens on map

Co-ordinates in Sherlock are frequently multiplied by 100.
Thus, on the overland map, the values can go up to 64000, which overflows
the signed 16-bit values allowed by the standard Common::Point class

engines/sherlock/map.h

@@ -68,7 +68,7 @@ class Map {
 	ImageFile *_shapes;
 	ImageFile *_iconShapes;
 	byte _sequences[MAX_HOLMES_SEQUENCE][MAX_FRAME];
-	Common::Point _lDrawnPos;
+	Point32 _lDrawnPos;
 	int _point;
 	bool _placesShown;
 	int _cursorIndex;
@@ -96,8 +96,8 @@ class Map {
 	void highlightIcon(const Common::Point &pt);
 public:
 	bool _active;
-	Common::Point _overPos;
-	Common::Point _bigPos;
+	Point32 _overPos;
+	Point32 _bigPos;
 	int _charPoint, _oldCharPoint;
 public:
 	Map(SherlockEngine *vm);

engines/sherlock/objects.cpp

@@ -184,7 +184,7 @@ void Sprite::checkSprite() {
 	Scene &scene = *_vm->_scene;
 	Screen &screen = *_vm->_screen;
 	Talk &talk = *_vm->_talk;
-	Common::Point pt;
+	Point32 pt;
 	Common::Rect objBounds;
 	Common::Point spritePt(_position.x / 100, _position.y / 100);
 

engines/sherlock/objects.h

@@ -79,6 +79,25 @@ enum {
 #define FLIP_CODE (64 + 128)
 #define SOUND_CODE (34 + 128)
 
+class Point32 {
+public:
+	int x;
+	int y;
+
+	Point32() : x(0), y(0) {}
+	Point32(int x1, int y1) : x(x1), y(y1) {}
+	Point32(const Common::Point &pt) : x(pt.x), y(pt.y) {}
+
+	bool operator==(const Point32 &p) const { return x == p.x && y == p.y; }
+	bool operator!=(const Point32 &p) const { return x != p.x || y != p.y; }
+	Point32 operator+(const Point32 &delta) const { return Point32(x + delta.x, y + delta.y); }
+	Point32 operator-(const Point32 &delta) const { return Point32(x - delta.x, y - delta.y); }
+	operator Common::Point() { return Common::Point(x, y); }
+
+	void operator+=(const Point32 &delta) { x += delta.x; y += delta.y; }
+	void operator-=(const Point32 &delta) { x -= delta.x; y -= delta.y; }
+};
+
 class Sprite {
 private:
 	static SherlockEngine *_vm;
@@ -95,8 +114,8 @@ class Sprite {
 	int _allow;							// Allowed menu commands - ObjectAllow
 	int _frameNumber;					// Frame number in rame sequence to draw
 	int _sequenceNumber;				// Sequence being used
-	Common::Point _position;			// Current position
-	Common::Point _delta;				// Momvement delta
+	Point32 _position;					// Current position
+	Point32 _delta;						// Momvement delta
 	Common::Point _oldPosition;			// Old position
 	Common::Point _oldSize;				// Image's old size
 	Common::Point _goto;				// Walk destination