Compiler warnings in host.c

Steps to reproduce:

1. Compile Zabbix server or proxy from source using -O2 -Wall

   Making all in zbxdbhigh
   host.c: In function ‘DBcopy_template_host_prototypes’:
   host.c:3360:80: warning: ‘host_prototype’ may be used uninitialized in this function [-Wmaybe-uninitialized]
        group_prototype = (zbx_group_prototype_t *)host_prototype->group_prototypes.values[i];
                                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
   host.c:3265:24: note: ‘host_prototype’ was declared here
     zbx_host_prototype_t *host_prototype;
                           ^~~~~~~~~~~~~~
   host.c:3227:47: warning: ‘host_prototype’ may be used uninitialized in this function [-Wmaybe-uninitialized]
       if (FAIL == (i = zbx_vector_uint64_bsearch(&host_prototype->lnk_templateids, templateid,
                                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   host.c:3140:24: note: ‘host_prototype’ was declared here
     zbx_host_prototype_t *host_prototype;
                           ^~~~~~~~~~~~~~
   

Result:

Expected:
No warnings. See host.patch.