fix: several crash causes Host subtabs when connection is lost externally

This also changes the dodgy default text "Node" in any VirtualTree's cell to "-"

Refs #1875

source/apphelpers.pas

@@ -1532,6 +1532,7 @@ begin
   VT.EndUpdate;
   VT.TextMargin := 6;
   VT.Margin := 2;
+  VT.DefaultText := '-'; // "Node" by default
   // Disable hottracking in non-Vista mode, looks ugly in XP, but nice in Vista
   if (toUseExplorerTheme in VT.TreeOptions.PaintOptions) and (Win32MajorVersion >= 6) then
     VT.TreeOptions.PaintOptions := VT.TreeOptions.PaintOptions + [toHotTrack]

source/main.pas

@@ -9456,6 +9456,8 @@ begin
   if Sender = ListProcesses then begin
     Idx := Sender.GetNodeData(Node);
     Results := GridResult(Sender);
+    if not Results.Connection.Active then
+      Exit;
     Results.RecNo := Idx^;
     case Kind of
       ikNormal, ikSelected: begin
@@ -9500,11 +9502,15 @@ var
 begin
   Idx := Sender.GetNodeData(Node);
   Results := GridResult(Sender);
-  // See issue #3416
-  if (Results = nil) and (Sender <> ListVariables) then
-    Exit;
-  if Results <> nil then
+
+  // See issue #3416. Note: ListVariables does not depend on a live result, but on a StringList.
+  if Sender <> ListVariables then begin
+    // See issue #1875
+    if (Results = nil) or (not Results.Connection.Active) then
+      Exit;
     Results.RecNo := Idx^;
+  end;
+
 
   if (Sender = ListStatus) and (Column in [1,2,3]) then begin
     CellText := Results.Col(1);