network: drop unneeded null-check for ip4 address

The pointer has already been dereferenced. Might have made more sense
to check if it's the empty string and treat that as error, but
nm_utils_ipaddr_valid also returns error on empty string so lets just
rely on the utility function doing the right thing here.

https://bugzilla.gnome.org/show_bug.cgi?id=708500

panels/network/connection-editor/ce-page-ip4.c

@@ -750,7 +750,7 @@ ui_to_setting (CEPageIP4 *page)
                         continue;
                 }
 
-                if (!text_address || !nm_utils_ipaddr_valid (AF_INET, text_address)) {
+                if (!nm_utils_ipaddr_valid (AF_INET, text_address)) {
                         widget_set_error (GTK_WIDGET (entry));
                         ret = FALSE;
                 } else {