[py23_test] pass os.environ copy instead of empty dict to avoid issue on Windows

Otherwise I get this:
Fatal Python error: Failed to initialize Windows random API (CryptoGen)

https://ci.appveyor.com/project/anthrotype/fonttools/build/job/qhf8d89or4d5hiyd

see: http://bugs.python.org/issue20614

Lib/fontTools/misc/py23_test.py

@@ -36,9 +36,11 @@ class OpenFuncWrapperTest(unittest.TestCase):
 		try:
 			with open(datafile, 'rb') as infile, \
 					tempfile.NamedTemporaryFile(delete=False) as outfile:
+				env = dict(os.environ)
+				env["PYTHONPATH"] = os.pathsep.join(sys.path)
 				check_call(
 					[sys.executable, script], stdin=infile, stdout=outfile,
-					env={"PYTHONPATH": os.pathsep.join(sys.path)})
+					env=env)
 			result = not filecmp.cmp(infile.name, outfile.name, shallow=False)
 		finally:
 			os.remove(script)