LP#1850547: eg-grid: disable filter controls while fetching data

LP#1850547: eg-grid: disable filter controls while fetching data

This avoids situations where the user who is quick on the mark
tries to set a filter condition but not see it take effect
when the original query returns results.

Sponsored-by: Evergreen Community Development Initiative
Sponsored-by: Georgia Public Library Service
Sponsored-by: Indiana State Library
Sponsored-by: C/W MARS
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Tiffany Little <tlittle@georgialibraries.org>
Signed-off-by: Bill Erickson <berickxx@gmail.com>