feature partitioning: fix bugs in iterate_unpack #118

Job	Run time
Automake Serial Minimal Build on Linux	1m 19s
Automake Serial With Clawpack Build on Linux	1m 48s
Automake Serial With Clawpack and HDF Build on Linux	1m 44s
Automake Serial With GeoClaw Build on Linux	1m 36s
Automake Serial With CudaClaw (CUDA 10.1) Build on Linux	3m 12s
Automake Serial With CudaClaw (CUDA 11.3) Build on Linux	3m 40s
Automake MPI Minimal Build on Linux	1m 55s
Automake MPI Debug With CXX Build on Linux	3m 43s
Automake MPI With Clawpack Build on Linux	2m 24s
Automake MPI With Clawpack and HDF Build on Linux	2m 33s
Automake MPI With GeoClaw Build on Linux	2m 7s
Automake MPI With CudaClaw (CUDA 10.1) Build on Linux	3m 4s
Automake MPI With CudaClaw (CUDA 11.3) Build on Linux	4m 22s
Automake MPI With ThunderEgg Build on Linux	5m 27s
	38m 54s

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