[Protobuf] Make MultiTarget result optional #311

Job	Run time
PhotonClient Build	40s
Gradle Build	4m 34s
Build Examples	3m 48s
Build Offline Docs	1m 13s
Photonlib - Build Docker - Athena	6m 21s
Photonlib - Build Host - Win64	6m 53s
Photonlib - Build Docker - Raspbian	6m 29s
Photonlib - Build Host - macOS	7m 21s
Photonlib - Build Docker - Aarch64	7m 2s
Photonlib - Build Host - Linux	4m 26s
Build fat JAR - Win64	3m 16s
Build fat JAR - macOS	2m 38s
Build fat JAR - Linux	1m 32s
Build fat JAR - macOSArm	3m 13s
Build fat JAR - LinuxArm32	1m 33s
Build fat JAR - LinuxArm64	2m 28s
Build image - ${{ matrix.image_url }}	0s
release	0s
	1h 3m 27s

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