transaction: modernize transaction_free()

src/core/transaction.c

@@ -1199,8 +1199,12 @@ Transaction *transaction_new(bool irreversible) {
         return tr;
 }
 
-void transaction_free(Transaction *tr) {
+Transaction *transaction_free(Transaction *tr) {
+        if (!tr)
+                return NULL;
+
         assert(hashmap_isempty(tr->jobs));
         hashmap_free(tr->jobs);
-        free(tr);
+
+        return mfree(tr);
 }

src/core/transaction.h

@@ -16,7 +16,7 @@ struct Transaction {
 };
 
 Transaction *transaction_new(bool irreversible);
-void transaction_free(Transaction *tr);
+Transaction *transaction_free(Transaction *tr);
 
 void transaction_add_propagate_reload_jobs(Transaction *tr, Unit *unit, Job *by, bool ignore_order, sd_bus_error *e);
 int transaction_add_job_and_dependencies(