Fix Map and ToLower

Author: migueldeicaza

NStack/strings/ustring.cs

@@ -1818,6 +1818,7 @@ static ustring Map (Func<uint, uint> mapping, ustring s, Action scanReset = null
 				var mapped = mapping (rune);
 				if (mapped == rune) {
 					nbytes++;
+					offset += size;
 					continue;
 				}
 				modified = true;

NStackTests/ustringTest.cs

@@ -25,6 +25,13 @@ public class UstringTest {
 		ustring kosme = ustring.Make (0xce, 0xba, 0xcf, 0x8c, 0xcf, 0x83, 0xce, 0xbc, 0xce, 0xb5);
 		ustring kosmex = ustring.Make (0xce, 0xba, 0xcf, 0x8c, 0xcf, 0x83, 0xce, 0xbc, 0xce, 0xb5, 0x41);
 
+		[Test]
+		public void ToLowerTest ()
+		{
+			var x = ustring.Make ("C-x");
+			var res = x.ToLower ();
+		}
+
 		[Test]
 		public void IComparableTests ()
 		{