Merge pull request #84 from BDisp/consolewidth-negative-fix

Fixes #83. Ustring ConsoleWidth must return the exactly character size or zero and not the Rune.ColumnWidth if it's negative.

Author: tig

NStack/strings/ustring.cs

@@ -1056,7 +1056,8 @@ public ustring RuneSubstring (int runeStart, int length = 0)
 		public int RuneCount => Utf8.RuneCount (this);
 
 		/// <summary>
-		/// Returns the number of columns used by the unicode string on console applications.  This is done by calling the Rune.ColumnWidth on each rune.
+		/// Returns the number of columns used by the unicode string on console applications. 
+		/// This is done by calling the Rune.ColumnWidth or zero, if it's negative, on each rune.
 		/// </summary>
 		public int ConsoleWidth {
 			get {
@@ -1065,7 +1066,7 @@ public int ConsoleWidth {
 				for (int i = 0; i < blen;) {
 					(var rune, var size) = Utf8.DecodeRune (this, i, i - blen);
 					i += size;
-					total += Rune.ColumnWidth (rune);
+					total += Math.Max (Rune.ColumnWidth (rune), 0);
 				}
 				return total;
 			}