Modules: fix out-of-bounds read when loading a shared dict file

Modules: fix out-of-bounds read when loading a shared dict file

Previously, ngx_js_dict_parse_entry() parsed numeric values with
strtod((char *) p, &p), which has no end awareness. The state
file loader allocated a buffer sized to the exact file length and
passed end = buf + len, so a numeric token whose digits ran to the
very end of the allocation (for example a truncated or tampered
state file ending in '"value":123') let strtod() read past the
buffer into adjacent pool memory.

NUL-terminate the loaded buffer so strtod() stops at the file end.