urlmatch: Disallow NUL byte

See https://bugs.chromium.org/p/chromium/issues/detail?id=390624
With Qt, we might run into the same issue as well at some point, and it sure
can't hurt to disallow it.

qutebrowser/utils/urlmatch.py

@@ -53,6 +53,9 @@ class UrlPattern:
             self._match_all = True
             return
 
+        if '\0' in pattern:
+            raise ValueError("May not contain NUL byte")
+
         # > If the scheme is *, then it matches either http or https, and not
         # > file, or ftp.
         # Note we deviate from that, as per-URL settings aren't security

tests/unit/utils/test_urlmatch.py

@@ -45,6 +45,9 @@ from qutebrowser.utils import urlmatch
     # FIXME: should we allow this or not?
     # ("http://bar", "URLPattern::"),
 
+    # Chromium: PARSE_ERROR_INVALID_HOST
+    ("http://\0www/", "May not contain NUL byte"),
+
     # Chromium: PARSE_ERROR_INVALID_HOST_WILDCARD
     ("http://*foo/bar", "Invalid host wildcard"),
     ("http://foo.*.bar/baz", "Invalid host wildcard"),