Fix memory leak in connection graph

When generating virtual connections to represent bus aliases, we need to
store the pointers for future deletion otherwise we will leak the memory

eeschema/connection_graph.cpp

@@ -1349,11 +1349,15 @@ void CONNECTION_GRAPH::generateBusAliasMembers()
                 wxString name = conn->FullLocalName();
 
                 CONNECTION_SUBGRAPH* new_sg = new CONNECTION_SUBGRAPH( this );
+
+                // This connection cannot form a part of the item because the item is not, itself
+                // connected to this subgraph.  It exists as part of a virtual item that may be connected
+                // to other items but is not in the schematic.
                 SCH_CONNECTION* new_conn = new SCH_CONNECTION( item, subgraph->m_sheet );
                 new_conn->SetGraph( this );
-
                 new_conn->SetName( name );
                 new_conn->SetType( CONNECTION_TYPE::NET );
+                subgraph->StoreImplicitConnection( new_conn );
                 int code = assignNewNetCode( *new_conn );
 
                 wxLogTrace( ConnTrace, wxS( "SG(%ld), Adding full local name (%s) with sg (%d) on subsheet %s" ), subgraph->m_code,

eeschema/connection_graph.h

@@ -89,7 +89,11 @@ public:
               m_hier_parent( nullptr )
     {}
 
-    ~CONNECTION_SUBGRAPH() = default;
+    ~CONNECTION_SUBGRAPH()
+    {
+        for( SCH_CONNECTION* connection : m_bus_element_connections )
+            delete connection;
+    }
 
     /**
      * Determines which potential driver should drive the subgraph.
@@ -162,6 +166,13 @@ public:
 
     void RemoveItem( SCH_ITEM* aItem );
 
+    // Use this to keep a connection pointer that is not owned by any item
+    // This will be destroyed with the subgraph
+    void StoreImplicitConnection( SCH_CONNECTION* aConnection )
+    {
+        m_bus_element_connections.insert( aConnection );
+    }
+
 private:
     wxString driverName( SCH_ITEM* aItem ) const;
 
@@ -251,6 +262,10 @@ public:
     /// A cache of escaped netnames from schematic items
     mutable std::unordered_map<SCH_ITEM*, wxString> m_driver_name_cache;
 
+    /// A cache of connections that are part of this subgraph but that don't have
+    /// an owning element (i.e. bus members)
+    std::set<SCH_CONNECTION*> m_bus_element_connections;
+
 };
 
 struct NET_NAME_CODE_CACHE_KEY