fix: reject stray pipe in sign by using [+-] character class

Inside a character class '|' is a literal, so [+|-] matched '+', '-', or
'|'. A leading pipe was captured as a sign and stripped, letting malformed
input like '|5m' parse to 300 instead of returning None. Restrict the
class to the two intended sign characters.

pytimeparse/tests/testtimeparse.py

@@ -83,6 +83,10 @@ class TestTimeparse(unittest.TestCase):
         self.assertEqual(timeparse.timeparse('- 32 m 1 s'), -1921)
         self.assertIsNone(timeparse.timeparse('32 m - 1 s'))
         self.assertIsNone(timeparse.timeparse('32 m + 1 s'))
+        # A stray pipe is not a valid sign and must not be silently accepted.
+        self.assertIsNone(timeparse.timeparse('|5m'))
+        self.assertIsNone(timeparse.timeparse('| 5m'))
+        self.assertIsNone(timeparse.timeparse('|1:24'))
 
     def test_timeparse_1(self):
         '''timeparse test case 1.'''