112282 - navigate back/fwd stops working in some cases. This is just a safety patch. r=radha sr=hewitt

docshell/shistory/src/nsSHistory.cpp

@@ -38,7 +38,7 @@
 #include "nsIPref.h"
 
 #define PREF_SHISTORY_SIZE "browser.sessionhistory.max_entries"
-static PRInt32  gHistoryMaxSize = 0;
+static PRInt32  gHistoryMaxSize = 50;
 
 enum HistCmd{
   HIST_CMD_BACK,