Fix out of bounds when narrowing wide chars

XtermSharp/ReflowNarrower.cs

@@ -41,6 +41,10 @@ namespace XtermSharp {
 
 				int lastLineLength = wrappedLines [wrappedLines.Count - 1].GetTrimmedLength ();
 				int [] destLineLengths = GetNewLineLengths (wrappedLines, oldCols, newCols);
+
+				if (destLineLengths.Length == 0)
+					continue;
+
 				int linesToAdd = destLineLengths.Length - wrappedLines.Count;
 
 				int trimmedLines;