[Protobuf] Make MultiTarget result optional #310

Job	Run time
Build Examples	3m 45s
Build Examples	3m 45s
PhotonClient Build	38s
PhotonClient Build	38s
Gradle Build	3m 30s
Gradle Build	3m 28s
Build Offline Docs	1m 18s
Build Offline Docs	1m 18s
Photonlib - Build Docker - Athena	5m 56s
Photonlib - Build Docker - Athena	5m 56s
Photonlib - Build Host - Win64	4m 51s
Photonlib - Build Host - Win64	4m 51s
Photonlib - Build Docker - Raspbian	6m 45s
Photonlib - Build Docker - Raspbian	6m 45s
Photonlib - Build Host - macOS	8m 40s
Photonlib - Build Host - macOS	8m 40s
Photonlib - Build Docker - Aarch64	6m 35s
Photonlib - Build Docker - Aarch64	6m 35s
Photonlib - Build Host - Linux	3m 49s
Photonlib - Build Host - Linux	3m 49s
Build fat JAR - ${{ matrix.artifact-name }}	0s
Build fat JAR - ${{ matrix.artifact-name }}	0s
Build image - ${{ matrix.image_url }}	0s
Build image - ${{ matrix.image_url }}	0s
release	0s
release	0s
	1h 31m 32s

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