handle cases where we have a node with width 0 when reporting grammar errors

Author: mhegazy

src/compiler/parser.ts

@@ -654,7 +654,7 @@ module ts {
         // applying some stricter checks on that node.
         function grammarErrorOnNode(node: Node, message: DiagnosticMessage, arg0?: any, arg1?: any, arg2?: any): void {
             var span = getErrorSpanForNode(node);
-            var start = skipTrivia(file.text, span.pos);
+            var start = span.end > span.pos ? skipTrivia(file.text, span.pos) : span.pos;
             var length = span.end - start;
 
             file.syntacticErrors.push(createFileDiagnostic(file, start, length, message, arg0, arg1, arg2));