Fix FindRow() to deal with null argument.

camino/src/history/nsSimpleGlobalHistory.cpp

@@ -2204,8 +2204,10 @@ nsSimpleGlobalHistory::FindRow(mdb_column aCol,
 
   if (!hasRow) return NS_ERROR_NOT_AVAILABLE;
   
+  if (aResult) {
     *aResult = row;
     (*aResult)->AddRef();
+  }
     
   return NS_OK;
 }