[tautschnig]

The three hostent models returned a pointer to a zero-initialised
struct hostent on the success path. Since h_addr_list was NULL,
code that walks the address list (the main use of these functions)
was never analysed, hiding reachable assertions (soundness bug).

POSIX.1-2017 netdb.h specifies h_addr_list as a pointer to an array
of pointers to network addresses, terminated by a null pointer. The
models now set h_name to a valid (empty) string, h_aliases to a
NULL-terminated list, and h_addr_list to a NULL-terminated list with
one 4-byte address entry.

Fixes #9312

Found by Jeroen Robben's specification-conformance pipeline (https://reports.robben.io/methodology/).

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