KUrlRequester::setAcceptMode() got introduced in KIO 5.33.0, but k3b specifies 5.21.0 as minimum version.
Modify the KUrlRequester's fileDialog() directly when using an older version to fix the compilation.
This is intended for the Applications/17.12 branch, I consider it a bug that k3b fails to compile with KIO < 5.33 even though it states 5.21.0 as minimum.