Make sure all bytes of the WAL file are initialized even if the checksums are

not being computed until commit due to WAL overwrite.

FossilOrigin-Name: 1f44a9bdc1577aed088d9b91882527228015dcd3

src/wal.c

@@ -708,6 +708,8 @@ static void walEncodeFrame(
 
     sqlite3Put4byte(&aFrame[16], aCksum[0]);
     sqlite3Put4byte(&aFrame[20], aCksum[1]);
+  }else{
+    memset(&aFrame[8], 0, 16);
   }
 }