After #598 execution's block prefetch sensibly slower on Windows

[AndreaLanfranchi]

  // Before #598
  INFO [04-04|07:50:29.325 UTC] Begin Execution                    from=14473539 to=14518056
 TRACE [04-04|07:50:30.980 UTC] Fetched blocks                     size=10240 in=1.655s  @block 14473539
 TRACE [04-04|08:13:01.425 UTC] Fetched blocks                     size=10240 in=1.783s  @block 14483779
 
  // After #598
  INFO [04-04|08:33:49.310 UTC] Begin Execution                    from=14473539 to=14518056
 TRACE [04-04|08:33:51.225 UTC] Fetched blocks                     size=10240 in=1.914s  @block 14473539
 TRACE [04-04|08:37:54.712 UTC] Fetched blocks                     size=10240 in=6.115s  @block 14483779
 TRACE [04-04|08:49:27.386 UTC] Fetched blocks                     size=10240 in=42.631s @block 14494019
 TRACE [04-04|08:58:47.985 UTC] Fetched blocks                     size=10240 in=43.400s @block 14504259