tool-effect: treat tiles outside of city boundary as dirt

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@892 d9718cc8-9f43-0410-858b-315f434eb58c

src/micropolisj/engine/ToolEffect.java

@@ -42,7 +42,9 @@ class ToolEffect implements ToolEffectIfc
 			return city.getTile(originX + dx, originY + dy);
 		}
 		else {
-			return CLEAR;
+			// tiles outside city's boundary assumed to be
+			// tile #0 (dirt).
+			return 0;
 		}
 	}
 

src/micropolisj/engine/ToolEffectIfc.java

@@ -12,6 +12,7 @@ public interface ToolEffectIfc
 {
 	/**
 	 * Gets the tile at a relative location.
+	 * @return a non-negative tile identifier
 	 */
 	int getTile(int dx, int dy);