virGetHostnameLocalhost: avoid FP NULL-ptr-deref from clang

* src/util/util.c (virGetHostnameLocalhost): Add an sa_assert
to tell clang it's ok to dereference "info" after a non-failing
getaddrinfo call.

src/util/util.c

@@ -2394,6 +2394,9 @@ char *virGetHostnameLocalhost(int allow_localhost)
         return NULL;
     }
 
+    /* Tell static analyzers about getaddrinfo semantics.  */
+    sa_assert (info);
+
     /* if we aren't allowing localhost, then we iterate through the
      * list and make sure none of the IPv4 addresses are 127.0.0.1 and
      * that none of the IPv6 addresses are ::1