## 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!

ee/clickhouse/models/property.py
elif operator == "not_icontains":
        value = "%{}%".format(prop.value)
        params = {"k{}_{}".format(prepend, idx): prop.key, "v{}_{}".format(prepend, idx): value}
        return (
            "AND NOT ({left} LIKE %(v{prepend}_{idx})s)".format(
                idx=idx, prepend=prepend, left=denormalized if is_denormalized else json_extract
            ),
            params,
        )
    elif operator == "regex":
        params = {"k{}_{}".format(prepend, idx): prop.key, "v{}_{}".format(prepend, idx): prop.value}
        return (
            "AND match({left}, %(v{prepend}_{idx})s)".format(
                idx=idx, prepend=prepend, left=denormalized if is_denormalized else json_extract
            ),
            params,
        )
    elif operator == "not_regex":
        params = {"k{}_{}".format(prepend, idx): prop.key, "v{}_{}".format(prepend, idx): prop.value}
        return (
            "AND NOT match({left}, %(v{prepend}_{idx})s)".format(
                idx=idx, prepend=prepend, left=denormalized if is_denormalized else json_extract
            ),
            params,
        )
    elif operator == "is_set":
        params = {"k{}_{}".format(prepend, idx): prop.key, "v{}_{}".format(prepend, idx): prop.value}
        if is_denormalized:
            return (
                "AND NOT isNull({left})".format(left=denormalized),