in_emitter: Fix single record chunks and respect mem_buf_limit pause #8857

Job	Run time
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, gcc)	12m 25s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, clang)	12m 8s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, gcc)	11m 40s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, clang)	11m 37s
run-ubuntu-unit-tests (-DFLB_SMALL=On, gcc)	11m 48s
run-ubuntu-unit-tests (-DFLB_SMALL=On, clang)	13m 1s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, gcc)	11m 59s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, clang)	11m 55s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, gcc)	12m 11s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, clang)	12m 40s
run-ubuntu-unit-tests (-DFLB_COVERAGE=On, gcc)	43m 20s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, gcc)	11m 41s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, clang)	11m 41s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, gcc)	11m 45s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, clang)	11m 57s
run-macos-unit-tests (-DFLB_JEMALLOC=Off)	11m 8s
run-macos-unit-tests (-DFLB_SANITIZE_MEMORY=On)	10m 46s
run-macos-unit-tests (-DFLB_SANITIZE_THREAD=On)	11m 8s
Unit tests (matrix)	1s
	4h 4m 51s

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