filterx/expr-regexp-common: avoid excessive zero initialization of FilterXReMatchState #1365

Job	Run time
create-source-tarball	1m 52s
create-packages / almalinux-8	3m 58s
create-packages / almalinux-9	7m 27s
create-packages / debian-bookworm	6m 29s
create-packages / debian-testing	6m 9s
create-packages / fedora-41	11m 32s
create-packages / ubuntu-noble	8m 38s
	46m 5s

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