Fixed bugs in the :matches match type.

src/lib-sieve/mcht-matches.c

src/lib-sieve/sieve-match-types.c

src/lib-sieve/sieve-match-types.h

src/testsuite/tests/extensions/variables/match.svtest

src/testsuite/tests/lexer.svtest

src/testsuite/tests/match-types/matches.svtest