MINOR: chunks: allocate the trash chunks before parsing the config

get_trash_chunk() is convenient also while parsing the config, better
allocate them early just like the global trash.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 0a39d22..579dbcc 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -609,6 +609,7 @@
 		if (global.tune.maxrewrite >= global.tune.bufsize / 2)
 			global.tune.maxrewrite = global.tune.bufsize / 2;
 		chunk_init(&trash, realloc(trash.str, global.tune.bufsize), global.tune.bufsize);
+		alloc_trash_buffers(global.tune.bufsize);
 	}
 	else if (!strcmp(args[0], "tune.maxrewrite")) {
 		if (*(args[1]) == 0) {