Alignment issues when using database mmapped from a file

I have received several reports from Rspamd users about crashes when using Hyperscan database that is mmapped from a file (to reduce memory footprint when using the same database from multiple workers). One of the reports with some details could be found [here](https://github.com/rspamd/rspamd/issues/4329).

In general, I [load](https://github.com/rspamd/rspamd/blob/master/src/libserver/hyperscan_tools.cxx#L303) a serialized database, then [dump](https://github.com/rspamd/rspamd/blob/master/src/libserver/hyperscan_tools.cxx#L317) it to a memory buffer (properly aligned) and then [mmap](https://github.com/rspamd/rspamd/blob/master/src/libserver/hyperscan_tools.cxx#L380) and cast to hs_database_t. The pointer of the database itself is properly aligned on page boundary as guaranteed by mmap. So far, I'm not quite sure about what's going on in this case.