fix compiler warning: 'dot_4' may be used uninitialized in this function

ares/acountry.c

@@ -551,6 +551,7 @@ static void find_country_from_cname(const char *cname, struct in_addr addr)
   z0 = tolower(cname[0]);
   z1 = tolower(cname[1]);
   ccopy = strdup(cname);
+  dot_4 = NULL;
 
   ver_1 = (z0 == 'z' && z1 == 'z' && !strcasecmp(cname+4,nerd_ver1));
   ver_2 = (is_addr(ccopy,&dot_4) && !strcasecmp(dot_4,nerd_ver2));