fix: Filter out empty params in QueryReducer

[jlucytan]

Scope

No asana ticket. @thecristen mentioned this in Slack.

https://www.mbta.com/departures/?route_id=Red&&direction_id=0&stop_id=place-sstat prod seems to hang indefinitely when I fail at typing and insert an extra & heheh

See slack thread for more details.

Implementation

QueryReducer fails when the URI param has an undefined value (e.g. mbta.com/?&& and mbta.com/?foo&). This PR filters out cases where the key name is empty and adds basic handling for undefined values (simply passes it through as undefined)

Screenshots

Before - page hangs due to the JS param parsing erroring

After - normal display

How to test

Visit a schedule finder 2.0 page with various unexpected params:

• && (empty key, no val) local link
• &foo& (present key, no val) local link
• &foo=& (present key, empty val) local link
  • this should not hang even before this PR
• &=bar& (empty key, present val) local link
  • this should not hang even before this PR, but the QueryReducer now strips this entry from the params
  • it may be good to go to other places where we use params to make sure they haven't been affected

verify that they no longer hang

[lvachon1]

Works great!