Fix bitwise negation in CollisionMatrix#clear()

Adds the missing bitwise AND to the clear() method in CollisionMatrix,
so any flags besides the one given are retained.

game/src/main/org/apollo/game/model/area/collision/CollisionMatrix.java

@@ -104,6 +104,18 @@ public final class CollisionMatrix {
 		return false;
 	}
 
+	/**
+	 * Completely blocks the tile at the specified coordinate pair, while optionally allowing projectiles
+	 * to pass through.
+	 *
+	 * @param x The x coordinate.
+	 * @param y The y coordinate.
+	 * @param impenetrable If projectiles should be permitted to traverse this tile.
+	 */
+	public void block(int x, int y, boolean impenetrable) {
+		set(x, y, impenetrable ? ALL_BLOCKED : ALL_MOBS_BLOCKED);
+	}
+
 	/**
 	 * Completely blocks the tile at the specified coordinate pair.
 	 *
@@ -123,7 +135,7 @@ public final class CollisionMatrix {
 	 * @param flag The CollisionFlag.
 	 */
 	public void clear(int x, int y, CollisionFlag flag) {
-		set(x, y, (byte) ~flag.asByte());
+		set(x, y, (byte) (matrix[indexOf(x, y)] & ~flag.asByte()));
 	}
 
 	/**