Pcbnew: List nets fix calculation speed

Similar to 6e5726613, we need to find net node count quickly without
iterating over all items in the board.

pcbnew/class_board.cpp

@@ -1019,14 +1019,16 @@ int BOARD::GetNumSegmZone() const
 }
 
 
-unsigned BOARD::GetNodesCount()
+unsigned BOARD::GetNodesCount( int aNet )
 {
     unsigned retval = 0;
     for( auto mod : Modules() )
     {
         for( auto pad : mod->Pads() )
-            if( pad->GetNetCode() > 0 )
+        {
+            if( ( aNet == -1 && pad->GetNetCode() > 0 ) || aNet == pad->GetNetCode() )
                 retval++;
+        }
     }
 
     return retval;

pcbnew/class_board.h

@@ -689,9 +689,10 @@ public:
 
     /**
      * Function GetNodesCount
+     * @param aNet Only count nodes belonging to this net
      * @return the number of pads members of nets (i.e. with netcode > 0)
      */
-    unsigned GetNodesCount();
+    unsigned GetNodesCount( int aNet = -1 );
 
     /**
      * Function GetUnconnectedNetCount

pcbnew/dialogs/dialog_select_net_from_list.cpp

@@ -136,9 +136,9 @@ void DIALOG_SELECT_NET_FROM_LIST::buildNetsList()
                 continue;
         }
 
-        unsigned nPads = m_brd->GetConnectivity()->GetPadCount( netcode );
+        unsigned nodes = m_brd->GetNodesCount( netcode );
 
-        if( !m_cbShowZeroPad->IsChecked() && nPads == 0 )
+        if( !m_cbShowZeroPad->IsChecked() && nodes == 0 )
             continue;
 
         if( m_netsListGrid->GetNumberRows() <= row_idx )
@@ -151,7 +151,7 @@ void DIALOG_SELECT_NET_FROM_LIST::buildNetsList()
 
         if( netcode )
         {
-            txt.Printf( wxT( "%u" ), nPads );
+            txt.Printf( wxT( "%u" ), nodes );
             m_netsListGrid->SetCellValue( row_idx, COL_NETINFO, txt );
         }
         else    // For the net 0 (unconnected pads), the pad count is not known