lib-sieve: sieve-storage - Use int for sieve_script_sequence_next() status result

src/lib-sieve/sieve-script.c

src/lib-sieve/sieve-script.h

src/lib-sieve/sieve-storage-private.h

src/lib-sieve/storage/dict/sieve-dict-script.c

src/lib-sieve/storage/dict/sieve-dict-storage.h

src/lib-sieve/storage/file/sieve-file-script-sequence.c

src/lib-sieve/storage/file/sieve-file-storage.h

src/lib-sieve/storage/ldap/sieve-ldap-script.c

src/lib-sieve/storage/ldap/sieve-ldap-storage.h

src/plugins/lda-sieve/lda-sieve-plugin.c