Fix CTOC reading logic for reading child ids

The readNullTerminatedString was being called with the wrong length argument.
Also fixed the tests because they were relying on ArrayFileReader not to throw on out of bounds exceptions.

src/ID3v2FrameReader.js

@@ -458,7 +458,7 @@ frameReaderFunctions['CTOC'] = function readTableOfContentsFrame(
   result.entryCount = data.getByteAt(offset);
   offset++;
   for (var i = 0; i < result.entryCount; i++) {
-    var childId = StringUtils.readNullTerminatedString(data.getBytesAt(offset, length));
+    var childId = StringUtils.readNullTerminatedString(data.getBytesAt(offset, length - (offset - originalOffset)));
     result.childElementIds.push(childId.toString());
     offset += childId.bytesReadCount;
   }

src/__tests__/ID3v2FrameReader-test.js

@@ -330,7 +330,15 @@ describe("ID3v2FrameReader", function() {
       [0b00000011], // toplevel/ordered bit
       [0x02], // entry count
       bin("ID2"), [0x00], // child 1
-      bin("ID3"), [0x00] // child 2
+      bin("ID3"), [0x00], // child 2
+      bin("TIT1"), // child 1
+        [0x00, 0x00, 0x00, 0x02], // size
+        [0x00, 0x00], // flags
+        [0x00, 0x00], // text encoding + null terminated string
+      bin("TIT2"), // child 2
+        [0x00, 0x00, 0x00, 0x02], // size
+        [0x00, 0x00], // flags
+        [0x00, 0x00] // text encoding + null terminated string
     );
     var fileReader = new ArrayFileReader(fileData);
     var data = frameReader(0, fileData.length, fileReader, null, {major: 3});
@@ -341,8 +349,21 @@ describe("ID3v2FrameReader", function() {
       ordered: true,
       entryCount: 2,
       childElementIds: [ "ID2", "ID3" ],
-      subFrames: {} }
-    );
+      subFrames: {
+        TIT1: {
+          data: '',
+          description: 'Content group description',
+          id: 'TIT1',
+          size: 2
+        },
+        TIT2: {
+          data: '',
+          description: 'Title/songname/content description',
+          id: 'TIT2',
+          size: 2
+        }
+      }
+    });
   });
 
   it("should read CHAP tag", function() {