Ensure we only look at SearchField records (not FilterField) to find boost values
Ensure we only look at SearchField records (not FilterField) to find boost values

It's valid for the same field to exist as both a SearchField and FilterField, and in this case get_boost would randomly find the FilterField and try (and fail) to read its 'boost' attribute.

timorieber/wagtail,timorieber/wagtail,timorieber/wagtail,mikedingjan/wagtail,jnns/wagtail,FlipperPA/wagtail,nimasmi/wagtail,nimasmi/wagtail,timorieber/wagtail,mixxorz/wagtail,mikedingjan/wagtail,nimasmi/wagtail,gasman/wagtail,wagtail/wagtail,nealtodd/wagtail,takeflight/wagtail,FlipperPA/wagtail,nealtodd/wagtail,kaedroho/wagtail,mikedingjan/wagtail,mikedingjan/wagtail,gasman/wagtail,jnns/wagtail,jnns/wagtail,FlipperPA/wagtail,rsalmaso/wagtail,thenewguy/wagtail,takeflight/wagtail,gasman/wagtail,nimasmi/wagtail,mixxorz/wagtail,kaedroho/wagtail,thenewguy/wagtail,nealtodd/wagtail,gasman/wagtail,thenewguy/wagtail,FlipperPA/wagtail,mixxorz/wagtail,mixxorz/wagtail,gasman/wagtail,mixxorz/wagtail,zerolab/wagtail,takeflight/wagtail,rsalmaso/wagtail,nealtodd/wagtail,torchbox/wagtail,wagtail/wagtail,torchbox/wagtail,torchbox/wagtail,torchbox/wagtail,kaedroho/wagtail,zerolab/wagtail,thenewguy/wagtail,wagtail/wagtail,rsalmaso/wagtail,zerolab/wagtail,thenewguy/wagtail,wagtail/wagtail,rsalmaso/wagtail,kaedroho/wagtail,rsalmaso/wagtail,wagtail/wagtail,zerolab/wagtail,takeflight/wagtail,jnns/wagtail,zerolab/wagtail,kaedroho/wagtail