network: is_ip_in_cidr: avoid warning when versions don't match

is_ip_in_cidr('fd80:1::10', '127.0.0.1/24') would result in
    Use of uninitialized value in numeric eq (==)
as overlaps() returns undef in such a case.

Note that there are (albeit few) existing callers that don't specify $version.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>

src/PVE/Network.pm

@@ -594,6 +594,8 @@ sub is_ip_in_cidr {
 
     my $overlap = $cidr_obj->overlaps($ip_obj);
 
+    return if !defined($overlap);
+
     return $overlap == $Net::IP::IP_B_IN_A_OVERLAP || $overlap == $Net::IP::IP_IDENTICAL;
 }