basic: make check-pointer-deref clean

Add the needed assert changes to make the code clean
for the new check-pointer-deref script.

Note that for `_cmp()` functions its a bit of a question
if we want `assert()` or `POINTER_MAY_BE_NULL()` here. The
former is more correct but it adds a (small) runtime hit. If
we use POINTER_MAY_BE_NULL() it is compiled out but strictly
speaking it is wrong (so at least we would need a comment).

src/basic/unit-def.c

@@ -24,6 +24,8 @@ int unit_name_from_dbus_path(const char *path, char **name) {
         const char *e;
         char *n;
 
+        assert(name);
+
         e = startswith(path, "/org/freedesktop/systemd1/unit/");
         if (!e)
                 return -EINVAL;