Fixed path when map_key is first element

gen->path always contains at least 1 element, and when a map_start event is
found a new None element is added to the list. Thus the logic to find whether
this map key is the first element of the prefix returned by this generator was
wrong and generated ".key" for a JSON like '{"key": 1}'

I've added a unit test to make sure this problem doesn't arise again.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

ijson/backends/_yajl2.c

@@ -504,7 +504,7 @@ static PyObject* parsegen_iternext(PyObject *self) {
 		// new_path = path_stack[-2] + to_append
 		PyObject *last_path;
 		N_N(last_path = PySequence_GetItem(gen->path, npaths-2));
-		if( npaths > 1 ) {
+		if( npaths > 2 ) {
 			PyObject *last_path_dot;
 			CONCAT(last_path_dot, last_path, dot);
 			last_path = last_path_dot;

tests.py

@@ -192,6 +192,12 @@ def test_api(self):
         self.assertTrue(list(self.backend.items(BytesIO(JSON), '')))
         self.assertTrue(list(self.backend.parse(BytesIO(JSON))))
 
+    def test_items_twodictlevels(self):
+        f = BytesIO(b'{"meta":{"view":{"columns":[{"id": -1}, {"id": -2}]}}}')
+        ids = list(self.backend.items(f, 'meta.view.columns.item.id'))
+        self.assertEqual(2, len(ids))
+        self.assertListEqual([-2,-1], sorted(ids))
+
 # Generating real TestCase classes for each importable backend
 for name in ['python', 'yajl', 'yajl2', 'yajl2_cffi', 'yajl2_c']:
     try:
@@ -265,7 +271,6 @@ def test_items(self):
             None,
         ])
 
-
 class Stream(unittest.TestCase):
     def test_bytes(self):
         l = Lexer(BytesIO(JSON))