## Bug description

The following filter fails with a 500 internal error.

![2021-02-04_12-07](https://user-images.githubusercontent.com/148820/106877644-a9f4ce80-66e1-11eb-8320-87bb213bdde2.png)


## Expected behavior

Error is shown to user about invalid regular expression.

Note no errors shown on the page as well.

## How to reproduce

1. Go to events
2. Add filter "Current URL matches regular expression ?*"
3. See infinite loading screen / error

## Environment

- [x] PostHog Cloud
- [x] self-hosted PostHog, version/commit: _please provide_

## Additional context

Note this can also happen when filtering by events.

#### *Thank you* for your bug report – we love squashing them!

posthog/models/property.py
if value == "true":
            return True
        if value == "false":
            return False
        if isinstance(value, int):
            return value
        try:
            return json.loads(value)
        except (json.JSONDecodeError, TypeError):
            return value
    def property_to_Q(self) -> Q:
        from .cohort import CohortPeople
        value = self._parse_value(self.value)
        if self.type == "cohort":
            return Q(Exists(CohortPeople.objects.filter(cohort_id=int(value), person_id=OuterRef("id"),).only("id")))
        if self.operator == "is_not":
            return Q(~Q(**{"properties__{}".format(self.key): value}) | ~Q(properties__has_key=self.key))
        if self.operator == "is_set":
            return Q(**{"properties__{}__isnull".format(self.key): False})
        if self.operator == "is_not_set":
            return Q(**{"properties__{}__isnull".format(self.key): True})
        if isinstance(self.operator, str) and self.operator.startswith("not_"):
            return Q(
                ~Q(**{"properties__{}__{}".format(self.key, self.operator[4:]): value})
                | ~Q(properties__has_key=self.key)
                | Q(**{"properties__{}".format(self.key): None})
            )
        return Q(**{"properties__{}{}".format(self.key, f"__{self.operator}" if self.operator else ""): value})