pcbnew: don't rebuild dynamic ratsnest when moving items without a net (e.g. board outlines)

Fixes: lp:1778321
* https://bugs.launchpad.net/kicad/+bug/1778321

pcbnew/connectivity_data.cpp

@@ -224,13 +224,44 @@ void CONNECTIVITY_DATA::FindIsolatedCopperIslands( std::vector<CN_ZONE_ISOLATED_
     m_connAlgo->FindIsolatedCopperIslands( aZones );
 }
 
+int CONNECTIVITY_DATA::countRelevantItems( const std::vector<BOARD_ITEM*>& aItems )
+{
+    int n = 0;
+
+    for( const auto item : aItems )
+    {
+        switch( item->Type() )
+        {
+            case PCB_TRACE_T:
+            case PCB_PAD_T:
+            case PCB_ZONE_AREA_T:
+            case PCB_MODULE_T:
+            case PCB_VIA_T:
+                n++;
+                break;
+            
+            default:
+                break;
+        }
+    }
+    
+    return n;
+}
+
+
 void CONNECTIVITY_DATA::ComputeDynamicRatsnest( const std::vector<BOARD_ITEM*>& aItems )
 {
+    if( countRelevantItems( aItems ) == 0 )
+    {
+        m_dynamicRatsnest.clear();
+        return ;
+    }
+
     m_dynamicConnectivity.reset( new CONNECTIVITY_DATA );
     m_dynamicConnectivity->Build( aItems );
 
     m_dynamicRatsnest.clear();
-
+    
     BlockRatsnestItems( aItems );
 
     for( unsigned int nc = 1; nc < m_dynamicConnectivity->m_nets.size(); nc++ )

pcbnew/connectivity_data.h

@@ -236,7 +236,8 @@ public:
     void SetProgressReporter( PROGRESS_REPORTER* aReporter );
 
 private:
-
+    
+    int countRelevantItems( const std::vector<BOARD_ITEM*>& aItems );
     void    updateRatsnest();
     void    addRatsnestCluster( const std::shared_ptr<CN_CLUSTER>& aCluster );