stage1: don't filter test blocks with empty label
stage1: don't filter test blocks with empty label

The common pattern of including a file containing all the tests in a
empty-label test block breaks down when using --test-filter.

zig-lang/zig,andrewrk/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig,zig-lang/zig,raulgrell/zig