## 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/utils.py
append: Dict[str, Any] = {}
    append["data"] = []
    append["labels"] = []
    append["days"] = []
    days_format = "%Y-%m-%d"
    if interval == "hour" or interval == "minute":
        days_format += " %H:%M:%S"
    for item in dates_filled:
        date = item[0]
        value = item[1]
        append["days"].append(date.strftime(days_format))
        append["labels"].append(format_label_date(date, interval))
        append["data"].append(value)
    if math == "sum":
        append["count"] = sum(append["data"])
    return append
def get_ip_address(request: HttpRequest) -> str:
    """ use requestobject to fetch client machine's IP Address """
    x_forwarded_for = request.META.get("HTTP_X_FORWARDED_FOR")
    if x_forwarded_for:
        ip = x_forwarded_for.split(",")[0]
    else:
        ip = request.META.get("REMOTE_ADDR")  
    return ip
def dict_from_cursor_fetchall(cursor):