Optimize itemset

When counting items, many cases exist where we want to count all items
without checking flags.  This short-circuits the loop to provide the
immediate count.

pcbnew/router/pns_itemset.h

@@ -120,6 +120,9 @@ public:
     {
         int n = 0;
 
+        if( aKindMask == -1 || aKindMask == ITEM::ANY_T )
+            return m_items.size();
+
         for( ITEM* item : m_items )
         {
             if( item->Kind() & aKindMask )