Open-Xchange: Null pointer dereference in lib-sieve after calling sieve_binary_block_index

There are some places that program calls function sievebinaryblockindex without checking the return valuemainly in sieve-binary-dumper.c. Such as: pigeonhole/src/lib-sieve/sieve-binary-dumper.c: bool sievebinarydumperrunstruct sievebinarydumper dumper, struct ostream stream, bool verbose struct...