Fix workspace usage after Varnish WS overhaul.

src/vmod_gcrypt.c

@@ -600,13 +600,13 @@ VCL_BLOB vmod_symmetric_decrypt(VRT_CTX,
 		return NULL;
 	}
 
-	plaintext->blob = plain = WS_Front(ctx->ws);
 	if (WS_ReserveAll(ctx->ws) < (unsigned) ciphertext->len) {
 		VERRNOMEM(ctx, "Allocating plaintext result in %s.decrypt()",
 			  symmetric->vcl_name);
 		WS_Reset(ctx->ws, snap);
 		return NULL;
 	}
+	plaintext->blob = plain = WS_Reservation(ctx->ws);
 
 	hd = get_symmetric_hd(ctx, symmetric, "decrypt");
 	if (hd == NULL)