Do not export an empty to path to a windows image config #3

Job	Run time
prepare	10s
binaries (darwin/amd64)	1m 2s
binaries (darwin/arm64)	1m 7s
binaries (linux/amd64)	2m 4s
binaries (linux/arm/v7)	1m 58s
binaries (linux/arm64)	2m 1s
binaries (linux/s390x)	1m 59s
binaries (linux/ppc64le)	1m 58s
binaries (linux/riscv64)	2m 20s
binaries (windows/amd64)	1m 34s
binaries (windows/arm64)	1m 52s
test / prepare	2m 2s
test / run (containerd, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	7m 27s
test / run (containerd-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integr...	8m 46s
test / run (containerd-1.6, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	8m 2s
test / run (containerd-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./fronte...	8m 9s
test / run (oci, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	5m 4s
test / run (oci-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	5m 0s
test / run (oci-rootless-slirp4netns-detachnetns, ./client ./cmd/buildctl ./worker/containerd ./solver ....	4m 51s
test / run (oci-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, int...	5m 4s
test / run (./..., 1, integration gateway)	4m 49s
test / run (./client, containerd, nydus, integration)	7m 14s
test / run (./client, oci, nydus, integration)	5m 15s
test / run (./..., nydus, 1, integration)	4m 34s
image	9m 5s
image (rootless)	9m 46s
release	9s
	1h 53m 22s

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