Fix broken assignment in deinit.

Add an extra test to prove that it's needed.
diff --git a/colorama/initialise.py b/colorama/initialise.py
index 7abeb1c..eb114b9 100644
--- a/colorama/initialise.py
+++ b/colorama/initialise.py
@@ -22,19 +22,16 @@
 
 
 def init(autoreset=False, convert=None, strip=None, wrap=True):
-
     if not wrap and any([autoreset, convert, strip]):
         raise ValueError('wrap=False conflicts with any other arg=True')
 
     global wrapped_stdout, wrapped_stderr
     global orig_stdout, orig_stderr
 
-    # Prevent multiple calls from losing the original stdout
-    if (
-        orig_stdout is UNSET and
-        orig_stderr is UNSET
-    ):
+    # Prevent multiple calls from losing the original stdout/err
+    if orig_stdout is UNSET:
         orig_stdout = sys.stdout
+    if orig_stderr is UNSET:
         orig_stderr = sys.stderr
 
     if sys.stdout is None:
@@ -58,10 +55,10 @@
     global orig_stdout, orig_stderr
     if orig_stdout is not UNSET:
         sys.stdout = orig_stdout
-        orig_stdout == UNSET
+        orig_stdout = UNSET
     if orig_stderr is not UNSET:
         sys.stderr = orig_stderr
-        orig_stderr == UNSET
+        orig_stderr = UNSET
 
 
 @contextlib.contextmanager
diff --git a/colorama/tests/initialise_test.py b/colorama/tests/initialise_test.py
index 24ad744..0aac36e 100644
--- a/colorama/tests/initialise_test.py
+++ b/colorama/tests/initialise_test.py
@@ -6,12 +6,14 @@
 from mock import patch
 
 from ..ansitowin32 import StreamWrapper
+from .. import initialise
 from ..initialise import deinit, init
 from .utils import osname, redirected_output, replace_by
 
 orig_stdout = sys.stdout
 orig_stderr = sys.stderr
 
+
 class InitTest(TestCase):
 
     def setUp(self):
@@ -21,6 +23,8 @@
     def tearDown(self):
         sys.stdout = orig_stdout
         sys.stderr = orig_stderr
+        initialise.orig_stdout = initialise.UNSET
+        initialise.orig_stderr = initialise.UNSET
 
     def assertWrapped(self):
         self.assertIsNot(sys.stdout, orig_stdout, 'stdout should be wrapped')
@@ -75,7 +79,7 @@
         self.assertRaises(ValueError, lambda: init(autoreset=True, wrap=False))
 
     @patch('colorama.ansitowin32.winapi_test', lambda *_: True)
-    def testInitTwiceCanUndoneWithDeinitOnce(self):
+    def testInitTwiceCanBeUndoneWithDeinitOnce(self):
         with osname('nt'):
             self.assertNotWrapped()
             init()
@@ -85,6 +89,21 @@
             deinit()
             self.assertNotWrapped()
 
+    @patch('colorama.ansitowin32.winapi_test', lambda *_: True)
+    def testInitDeinitInitWorks(self):
+        with osname('nt'):
+            self.assertNotWrapped()
+            init()
+            self.assertWrapped()
+            deinit()
+            self.assertNotWrapped()
+            init()
+            self.assertWrapped()
+            deinit()
+            self.assertNotWrapped()
+            init()
+            self.assertWrapped()
+
     @patch('colorama.win32.SetConsoleTextAttribute')
     @patch('colorama.initialise.AnsiToWin32')
     def testAutoResetPassedOn(self, mockATW32, _):