DAOS-13806 common: refine NULL buf case in daos_sgl_processor (#12519) #4316

Job	Run time
Build DAOS (alma.8)	1h 18m 6s
Build DAOS (alma.9)	59m 8s
Build DAOS (rocky.8)	1h 11m 4s
Build DAOS (ARM64) (ubuntu, clang)	48m 1s
Build DAOS (ARM64) (alma.8, clang)	51m 40s
Build DAOS (ARM64) (leap.15, clang)	53m 16s
Create Docker images (ubuntu)	23m 24s
Create Docker images (rocky)	20m 45s
Create Docker images (fedora)	19m 44s
Create Docker images (leap.15)	22m 15s
Run DAOS/NLT tests (ubuntu)	22m 50s
Build DAOS in image (ubuntu, clang)	28m 58s
Build DAOS in image (ubuntu, gcc)	24m 0s
Build DAOS in image (rocky, clang)	23m 10s
Build DAOS in image (rocky, gcc)	28m 43s
Build DAOS in image (fedora, clang)	19m 23s
Build DAOS in image (fedora, gcc)	24m 12s
Build DAOS in image (leap.15, clang)	19m 12s
Build DAOS in image (leap.15, gcc)	20m 22s
	10h 58m 13s

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