pack: do not multiply out_size by realloc_size #9801

Job	Run time
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, gcc)	13m 31s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, clang)	13m 30s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, gcc)	12m 43s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, clang)	12m 48s
run-ubuntu-unit-tests (-DFLB_SMALL=On, gcc)	13m 1s
run-ubuntu-unit-tests (-DFLB_SMALL=On, clang)	13m 43s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, gcc)	12m 57s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, clang)	13m 0s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, gcc)	13m 8s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, clang)	13m 4s
run-ubuntu-unit-tests (-DFLB_COVERAGE=On, gcc)	46m 12s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, gcc)	12m 46s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, clang)	12m 58s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, gcc)	12m 41s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, clang)	13m 12s
run-macos-unit-tests (-DFLB_JEMALLOC=Off)	12m 45s
run-macos-unit-tests (-DFLB_SANITIZE_MEMORY=On)	12m 19s
run-macos-unit-tests (-DFLB_SANITIZE_THREAD=On)	12m 9s
Unit tests (matrix)	1s
	4h 26m 28s

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