Make sure readInt doesn't try to read past len, if given

Issue #15

acorn.js

@@ -673,7 +673,7 @@
 
   function readInt(radix, len) {
     var start = tokPos, total = 0;
-    for (;;) {
+    for (var i = 0, e = len == null ? Infinity : len; i < e; ++i) {
       var code = input.charCodeAt(tokPos), val;
       if (code >= 97) val = code - 97 + 10; // a
       else if (code >= 65) val = code - 65 + 10; // A

index.html

@@ -451,7 +451,7 @@ here (don't ask).</p>             </td>             <td class="code">
 were read, the integer value otherwise. When <code>len</code> is given, this
 will return <code>null</code> unless the integer has exactly <code>len</code> digits.</p>             </td>             <td class="code">               <div class="highlight"><pre>  <span class="kd">function</span> <span class="nx">readInt</span><span class="p">(</span><span class="nx">radix</span><span class="p">,</span> <span class="nx">len</span><span class="p">)</span> <span class="p">{</span>
     <span class="kd">var</span> <span class="nx">start</span> <span class="o">=</span> <span class="nx">tokPos</span><span class="p">,</span> <span class="nx">total</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
-    <span class="k">for</span> <span class="p">(;;)</span> <span class="p">{</span>
+    <span class="k">for</span> <span class="p">(</span><span class="kd">var</span> <span class="nx">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="nx">e</span> <span class="o">=</span> <span class="nx">len</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">?</span> <span class="kc">Infinity</span> <span class="o">:</span> <span class="nx">len</span><span class="p">;</span> <span class="nx">i</span> <span class="o">&lt;</span> <span class="nx">e</span><span class="p">;</span> <span class="o">++</span><span class="nx">i</span><span class="p">)</span> <span class="p">{</span>
       <span class="kd">var</span> <span class="nx">code</span> <span class="o">=</span> <span class="nx">input</span><span class="p">.</span><span class="nx">charCodeAt</span><span class="p">(</span><span class="nx">tokPos</span><span class="p">),</span> <span class="nx">val</span><span class="p">;</span>
       <span class="k">if</span> <span class="p">(</span><span class="nx">code</span> <span class="o">&gt;=</span> <span class="mi">97</span><span class="p">)</span> <span class="nx">val</span> <span class="o">=</span> <span class="nx">code</span> <span class="o">-</span> <span class="mi">97</span> <span class="o">+</span> <span class="mi">10</span><span class="p">;</span> <span class="c1">// a</span>
       <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="nx">code</span> <span class="o">&gt;=</span> <span class="mi">65</span><span class="p">)</span> <span class="nx">val</span> <span class="o">=</span> <span class="nx">code</span> <span class="o">-</span> <span class="mi">65</span> <span class="o">+</span> <span class="mi">10</span><span class="p">;</span> <span class="c1">// A</span>

test/tests.js

@@ -26016,6 +26016,19 @@ test("a\u2028b", {
   ]
 });
 
+test("'a\\u0026b'", {
+  type: "Program",
+  body: [
+    {
+      type: "ExpressionStatement",
+      expression: {
+        type: "Literal",
+        value: "a\u0026b"
+      }
+    }
+  ]
+});
+
 // Failure tests
 
 testFail("{",