BUG/MEDIUM: map: Fix memory leak in the map converter

The allocated trash chunk is not freed properly and causes a memory leak
exhibited as the growth in the trash pool allocations. Bug was introduced
in commit 271022 (BUG/MINOR: map: fix map_regm with backref).

This should be backported to all branches where the above commit was
backported.

src/map.c

@@ -207,6 +207,8 @@ static int sample_conv_map(const struct arg *arg_p, struct sample *smp, void *pr
 				                  tmptrash->area,
 				                  pat->data->u.str.area,
 				                  (regmatch_t *)smp->ctx.a[0]);
+				free_trash_chunk(tmptrash);
+
 				if (len == -1)
 					return 0;