geocoding can fail when moving location to a nearby city

[alanb2718]

A user encountered the following bug, in which geocoding can fail when moving a meeting's location to a nearby city. The bug is reproducible. This is using version 3.0.4, with $county_auto_geocoding_enabled and $zip_auto_geocoding_enabled both set to true.

To reproduce:

1. Create a new meeting at this location:
   Destiny Center Church
   790 Sutro St
   Reno, NV

2. Change the location to
   American Legion Hall
   730 4th St
   Sparks, NV

After Step 1, the zip code is 89512, which is correct; and the lat and longitude are also correct for Destiny Center Church.

After Step 2, the zip code ought to be changed to 89431 but it's still (incorrectly) 89512. Also the lat and longitude is for 730 E 4th St, Reno (or very near); which does have the zip code 89512. So somehow the geocoder is getting stuck in Reno.

If I start with Destiny Center Church in Reno, then change the location to the Alano Club in Sparks, and then to the American Legion Hall in Sparks, the zip code, lat, and longitude are all correct for the American Legion.

It may not be worth trying to fix this in the old UI; but it would make a good unit test for the new UI, to make sure it works there.