[xml mode] Don't accept < characters not followed by tag name

Closes #962

Author: marijnh

mode/xml/xml.js

@@ -70,11 +70,12 @@ CodeMirror.defineMode("xml", function(config, parserConfig) {
         return "meta";
       }
       else {
-        type = stream.eat("/") ? "closeTag" : "openTag";
-        stream.eatSpace();
+        var isClose = stream.eat("/");
         tagName = "";
         var c;
         while ((c = stream.eat(/[^\s\u00a0=<>\"\'\/?]/))) tagName += c;
+        if (!tagName) return "error";
+        type = isClose ? "closeTag" : "openTag";
         state.tokenize = inTag;
         return "tag";
       }