settings: Hide save-discard widget correctly when setting is not changed.
settings: Hide save-discard widget correctly when setting is not changed.

This commit fixes the bug where save-discard was not hidden when message
edit or delete setting is first changed from "Anytime" to any other value
and then again to "Any time". The save-discard widget should be hidden
since the setting is value was "Any time" already.

The bug was because check_property_changed returned true for
"realm_message_content_edit_limit_minutes" and
"realm_message_content_delete_limit_minutes" for above case as value of
setting in page_params for "Any time" case is "null" and
get_input_element_value returned "undefined" as the custom input box is
empty for "Any time" case.

This bug was introduced in #21837 where we changed the input box to be
empty for "Any time" case.

andersk/zulip,zulip/zulip,andersk/zulip,andersk/zulip,andersk/zulip,rht/zulip,rht/zulip,rht/zulip,zulip/zulip,andersk/zulip,zulip/zulip,zulip/zulip,rht/zulip,andersk/zulip,rht/zulip,rht/zulip,rht/zulip,andersk/zulip,zulip/zulip,zulip/zulip,zulip/zulip