ogr_core.h: only ignore -Wfloat-equal for IsInit() and not for the rest of the file and files that include it (#5299)

git-svn-id: https://svn.osgeo.org/gdal/trunk@27791 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_vc12