DM: fix `--config $VIA-pdf` to not crash

dm/DM.cpp

Index: dm/DM.cpp
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 4df4f5861b09b42372a70ff0ef81757b21c98a24..7903c54a21af914b38aabfacef1d631c56806e49 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -643,7 +643,7 @@ static Sink* create_sink(const char* tag) {
 }
 
 static Sink* create_via(const char* tag, Sink* wrapped) {
-#define VIA(t, via, ...) if (0 == strcmp(t, tag)) { return new via(__VA_ARGS__); }
+#define VIA(t, via, ...) if (0 == strcmp(t, tag)) { return new via(t, __VA_ARGS__); }
     VIA("twice",     ViaTwice,             wrapped);
     VIA("pipe",      ViaPipe,              wrapped);
     VIA("serialize", ViaSerialization,     wrapped);