venti/wrarena: fix arenapart breakage

R=rsc
https://codereview.appspot.com/7027044
diff --git a/src/cmd/venti/srv/wrarena.c b/src/cmd/venti/srv/wrarena.c
index 39185ca..1e274ca 100644
--- a/src/cmd/venti/srv/wrarena.c
+++ b/src/cmd/venti/srv/wrarena.c
@@ -181,12 +181,11 @@
 	part = initpart(file, OREAD);
 	if(part == nil)
 		sysfatal("can't open file %s: %r", file);
-	initdcache(8 * MaxDiskBlock);
 
 	// Try as arena partition.
 	arena = nil;
 	ap = initarenapart(part);
-	if(ap == nil)
+	if(ap != nil)
 		goto loaded;
 
 	if(readpart(part, aoffset, buf, sizeof buf) < 0)
@@ -214,12 +213,14 @@
 		if(vtconnect(z) < 0)
 			sysfatal("vtconnect: %r");
 	}
-	
+
 	print("%T starting to send data\n");
 	c = chancreate(sizeof(ZClump), 0);
 	for(i=0; i<12; i++)
 		vtproc(vtsendthread, nil);
 
+	initdcache(8 * MaxDiskBlock);
+
 	if(ap != nil) {
 		for(i=0; i<ap->narenas; i++)
 			rdarena(ap->arenas[i], 0);