tree-wide: introduce mfree()

Pretty trivial helper which wraps free() but returns NULL, so we can
simplify this:
        free(foobar);
        foobar = NULL;
to this:
        foobar = mfree(foobar);

1 files changed, 1 insertions, 2 deletions

diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index 073cc77711..355c4f1ee3 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -1259,8 +1259,7 @@ static int add_units(sd_journal *j) {
                 }
         }
 
-        strv_free(patterns);
-        patterns = NULL;
+        patterns = strv_free(patterns);
 
         STRV_FOREACH(i, arg_user_units) {
                 _cleanup_free_ char *u = NULL;