tree-wide: initialize row/column explicitly before calling sd_json_parse_file()

The variables are error return parameters, i.e. only initialized on some errors,
not all. Let's hence always zero initialize them.

src/network/networkd-serialize.c

@@ -442,7 +442,7 @@ int manager_deserialize(Manager *manager) {
                 return log_debug_errno(errno, "Failed to fdopen() serialization file descriptor: %m");
 
         _cleanup_(sd_json_variant_unrefp) sd_json_variant *v = NULL;
-        unsigned err_line, err_column;
+        unsigned err_line = 0, err_column = 0;
         r = sd_json_parse_file(
                         f,
                         /* path = */ NULL,