bcachefs: Move alloc assertion to .key_invalid()

.key_invalid is a better place for this assertion.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/alloc_background.c

@@ -361,6 +361,14 @@ int bch2_alloc_v4_invalid(const struct bch_fs *c, struct bkey_s_c k,
 			pr_buf(err, "cached bucket with read_time == 0");
 			return -EINVAL;
 		}
+
+		if (!a.v->dirty_sectors &&
+		    !a.v->cached_sectors &&
+		    !a.v->stripe &&
+		    a.v->data_type) {
+			pr_buf(err, "empty, but data_type nonzero");
+			return -EINVAL;
+		}
 	}
 
 	return 0;

fs/bcachefs/alloc_background.h

@@ -44,7 +44,6 @@ static inline enum bucket_state bucket_state(struct bch_alloc_v4 a)
 		return BUCKET_dirty;
 	if (a.cached_sectors)
 		return BUCKET_cached;
-	BUG_ON(a.data_type);
 	if (BCH_ALLOC_V4_NEED_DISCARD(&a))
 		return BUCKET_need_discard;
 	if (alloc_gc_gen(a) >= BUCKET_GC_GEN_MAX)