[common] Fix candidate filtering.

The filtering was done on the thruthiness of the symbol
string content.
4 jobs for fix_no_change_filtering in 4 minutes and 1 second (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build_linux_36 #195134
docker-build

00:02:54

55.0%
passed build_linux_37 #195135
docker-build

00:02:47

55.0%
passed build_macosx_36 #195132
macosx

00:04:00

55.0%
passed build_macosx_37 #195133
macosx

00:03:47

55.0%