HLS: Ignore empty NALU to avoid error. v6.0.65 (#3750) #2608

Job	Run time
utest-regression-blackbox-test	6m 51s
cygwin64-cache	3m 51s
multiple-arch-aarch64	7m 58s
multiple-arch-armv7	11m 1s
cygwin64	15m 44s
fast	1s
build-ubuntu16	2m 25s
build-ubuntu18	2m 15s
build-centos7	3m 45s
build-ubuntu20	2m 28s
build-cross-aarch64	8m 17s
build-cross-arm	8m 10s
coverage	4m 25s
multiple-arch-amd64	1m 50s
test-done	1s
	1h 19m 2s

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