Do not run empty kernels (`num_tokens=0`) (#1141) #819

Job	Run time
Build and Install FlexFlow in a Docker Container (cuda, 11.1)	2h 14m 25s
Build and Install FlexFlow in a Docker Container (cuda, 11.2)	2h 19m 22s
Build and Install FlexFlow in a Docker Container (cuda, 11.3)	1h 52m 51s
Build and Install FlexFlow in a Docker Container (cuda, 11.4)	1h 59m 3s
Build and Install FlexFlow in a Docker Container (cuda, 11.5)	2h 13m 11s
Build and Install FlexFlow in a Docker Container (cuda, 11.6)	2h 15m 7s
Build and Install FlexFlow in a Docker Container (cuda, 11.7)	2h 21m 25s
Build and Install FlexFlow in a Docker Container (cuda, 11.8)	2h 5m 33s
Build and Install FlexFlow in a Docker Container (cuda, 12.0)	2h 25m 52s
Build and Install FlexFlow in a Docker Container (hip_rocm, 5.3)	5h 41m 49s
Build and Install FlexFlow in a Docker Container (hip_rocm, 5.4)	6h 0m 14s
Build and Install FlexFlow in a Docker Container (hip_rocm, 5.5)	6h 0m 14s
Build and Install FlexFlow in a Docker Container (hip_rocm, 5.6)	6h 0m 15s
Notify Slack in case of failure	0s
	1d 19h 29m 21s

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