Fix frames leak when VfsPoll fails

VfsPoll can fail to acquire the WAL write lock, and the caller still
needs to release the frames of the transaction in this case. Restores
the behavior from before the exec_tick rewrite.

Signed-off-by: Cole Miller <[email protected]>

src/leader.c

@@ -467,7 +467,7 @@ static int exec_apply(struct exec *req)
 
 	rv = VfsPoll(vfs, db->path, &frames, &n);
 	if (rv != 0) {
-		return rv;
+		goto finish;
 	}
 	sm_move(&req->sm, EXEC_POLLED);
 	if (n == 0) {