Proximity filter in view stops working when adding another exposed filter from another field.

Problem/Motivation

The steps to reproduce this issue may be somewhat convoluted but here's the best description I could come up with:

drupal core 7.20
geofield 7.x-2.0-alpha2+7-dev
views 7.x-3.5+42-dev

Created a content view with proximity filter set to less than 10 miles from geofield on entity from url used as source. When adding an exposed filter on another (taxonomy) field, the proximity values were no longer correctly replaced on the query's placeholders.

Proposed resolution

Traced the problem to an empty array key being evaluated as non empty. The attached patch fixed the issue for our case. It's a single line change so it can be easily applied manually in case the patch does not apply automatically.

Remaining tasks

To be further tested.