Fix IndexOutOfRangeException while parsing fenced code block with a single trailing space (#276)

src/Markdig.Tests/TestParser.cs

@@ -27,6 +27,13 @@ namespace Markdig.Tests
             TestSpec(input, "<p>9&amp;ddr;&amp;*&amp;ddr;&amp;de<64><65>__</p>");
         }
 
+        [Test]
+        public void TestInvalidCodeEscape()
+        {
+            var input = "```**Header**	";
+            var html = Markdown.ToHtml(input);
+        }
+
         [Test]
         public void TestEmphasisAndHtmlEntity()
         {

src/Markdig/Parsers/FencedBlockParserBase.cs

@@ -94,7 +94,7 @@ namespace Markdig.Parsers
 
                 // Skip any spaces after info string
                 firstSpace++;
-                while (true)
+                while (firstSpace <= line.End)
                 {
                     c = line[firstSpace];
                     if (c.IsSpaceOrTab())