[Protobuf] Make MultiTarget result optional #316

Job	Run time
PhotonClient Build	40s
Build Offline Docs	47s
Gradle Build	4m 6s
Build Examples	4m 41s
Photonlib - Build Docker - Athena	6m 44s
Photonlib - Build Docker - Raspbian	6m 52s
Photonlib - Build Host - Win64	6m 29s
Photonlib - Build Host - macOS	9m 46s
Photonlib - Build Docker - Aarch64	6m 38s
Photonlib - Build Host - Linux	3m 59s
Build fat JAR - Win64	2m 57s
Build fat JAR - macOS	2m 5s
Build fat JAR - Linux	1m 33s
Build fat JAR - macOSArm	3m 22s
Build fat JAR - LinuxArm32	2m 19s
Build fat JAR - LinuxArm64	2m 29s
Build image - ${{ matrix.image_url }}	0s
release	0s
	1h 5m 27s

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