Fix assertion failure

src/libutil/hash.cc

@@ -121,7 +121,7 @@ const string base32Chars = "0123456789abcdfghijklmnpqrsvwxyz";
 
 string printHash32(const Hash & hash)
 {
-    assert(hash.type != htUnknown);
+    assert(hash.hashSize);
     size_t len = hash.base32Len();
     assert(len);