Prevent errors when parsing date on malformed lines

We observed lines in our logs where the timestamp field was still
respecting the timestamp regexp, so the line was not reported as
invalid, but parsing such timestamp caused a ValueError in
_matchToDateTime

The beginning of line was:
127.0.0.1 - - [14/Jul/2017:127.0.0.1 - - [14/Jul/2017:09:41:41 +0200]

Which uses `[14/Jul/2017:127.0.0.1 - - [14/Jul/2017:09:41:41 +0200]` as
timestamp, so this fail the simple .split() used to separate timestamp
and timezone.

Added a minimal test case to reproduce this specific problem.

apachedex/__init__.py

@@ -764,7 +764,7 @@ logformat_dict = {
   '%b': r'(?P<bytes>[0-9-]*?)',
   '%l': r'(?P<ident>[^ ]*)',
   '%u': r'(?P<user>[^ ]*)',
-  '%t': r'\[(?P<timestamp>[^\]]*)\]',
+  '%t': r'\[(?P<timestamp>\d{2}/\w{3}/\d{4}:\d{2}:\d{2}:\d{2} [+-]\d{4})\]',
   '%r': r'(?P<request>[^"]*)', # XXX: expected to be enclosed in ". See also REQUEST_PATTERN
   '%>s': r'(?P<status>[0-9]*?)',
   '%O': r'(?P<size>[0-9-]*?)',

apachedex/tests.py

+import unittest
+import sys
+from StringIO import StringIO
+import apachedex
+
+
+class MalformedInputTestCase(unittest.TestCase):
+  def setUp(self):
+    self._original_sys_argv = sys.argv
+    self._original_sys_stdin = sys.stdin
+    self._original_sys_stderr = sys.stderr
+    self._original_sys_stdout = sys.stdout
+    sys.stderr = StringIO()
+    sys.stdout = StringIO()
+
+  def tearDown(self):
+    sys.argv = self._original_sys_argv
+    sys.stdin = self._original_sys_stdin
+    sys.stderr = self._original_sys_stderr
+    sys.stdout = self._original_sys_stdout
+
+  def test_timestamp_mixed_in_timestamp(self):
+    sys.argv = ['apachedex', '--base=/', '-']
+    sys.stdin = StringIO(
+    # this first line is valid, but second is not
+    '''127.0.0.1 - - [14/Jul/2017:09:41:41 +0200] "GET / HTTP/1.1" 200 7499 "https://example.org/" "Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36" 1754
+127.0.0.1 - - [14/Jul/2017:127.0.0.1 - - [14/Jul/2017:09:41:41 +0200] "GET / HTTP/1.1" 200 7499 "https://example.org/" "Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36" 1754''')
+    apachedex.main()
+
+    self.assertNotIn('Malformed line at -:1', sys.stderr.getvalue())
+    self.assertIn('Malformed line at -:2', sys.stderr.getvalue())
+