Fix performance test for block verification.

qa/zcash/performance-measurements.sh

@@ -108,7 +108,7 @@ case "$1" in
                 ;;
             validatelargetx)
                 zcashd_generate
-                zcash_rpc zcbenchmark validatelargetx 10
+                zcash_rpc zcbenchmark validatelargetx 2
                 ;;
             *)
                 zcashd_stop

src/zcbenchmarks.cpp

@@ -241,6 +241,7 @@ processblock:
     // 4) Call CreateNewBlock (which itself calls TestBlockValidity)
     pblocktemplate = CreateNewBlock(scriptDummy);
     pblock = &pblocktemplate->block;
+    pindexPrev = chainActive.Tip();
 
     // 5) Call TestBlockValidity again under timing
     timer_start();