Disable book during analysis

It is still enabled during fixed limit search so to
use it during fixed depth/nodes/time matches.

Bug reported by Daylen.

No functional changes.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/search.cpp

@@ -265,7 +265,7 @@ void Search::think() {
       goto finalize;
   }
 
-  if (Options["OwnBook"])
+  if (Options["OwnBook"] && !Limits.infinite)
   {
       Move bookMove = book.probe(pos, Options["Book File"], Options["Best Book Move"]);