use [-1] instead of endswith() to work with bytes or string

Also add a parametrize on decode_unicode for iter_lines() test
to check with bytestrings and str content

requests/models.py

@@ -813,7 +813,7 @@ def iter_lines(self, chunk_size=ITER_CHUNK_SIZE, decode_unicode=None, delimiter=
             #
             # If we're using `splitlines()`, we only do this if the chunk
             # ended midway through a line.
-            incomplete_line = lines[-1] and lines[-1].endswith(chunk[-1])
+            incomplete_line = lines[-1] and lines[-1][-1] == chunk[-1]
             if delimiter or incomplete_line:
                 pending = lines.pop()
 

tests/test_requests.py

@@ -1816,11 +1816,12 @@ def test_json_param_post_should_not_override_data_param(self, httpbin):
         prep = r.prepare()
         assert 'stuff=elixr' == prep.body
 
-    def test_response_iter_lines(self, httpbin):
+    @pytest.mark.parametrize('decode_unicode', (True, False))
+    def test_response_iter_lines(self, httpbin, decode_unicode):
         r = requests.get(httpbin('stream/4'), stream=True)
         assert r.status_code == 200
-
-        it = r.iter_lines()
+        r.encoding = 'utf-8'
+        it = r.iter_lines(decode_unicode=decode_unicode)
         next(it)
         assert len(list(it)) == 3