Fix unwanted enabling FModified flag in user manager dialog, when jus…

…t switching the main tab to "Limitations", followed by a crash due to no focused user. Closes #493.

source/usermanager.pas

@@ -412,16 +412,19 @@ procedure TUserManagerForm.Modification(Sender: TObject);
 var
   User: PUser;
 begin
-  if Assigned(listUsers.FocusedNode) and (TWinControl(Sender).Parent = tabLimitations) then begin
+  if not Assigned(listUsers.FocusedNode) then
+    Exit;
+  if TWinControl(Sender).Parent = tabLimitations then begin
     // Any TUpDown triggers a OnChange event on its TEdit when the UpDown gets painted
     User := listUsers.GetNodeData(listUsers.FocusedNode);
     Modified := Modified
       or (editMaxQueries.Text <> IntToStr(User.MaxQueries))
       or (editMaxUpdates.Text <> IntToStr(User.MaxUpdates))
       or (editMaxConnections.Text <> IntToStr(User.MaxConnections))
       or (editMaxUserConnections.Text <> IntToStr(User.MaxUserConnections));
-  end else
+  end else begin
     Modified := True;
+  end;
 end;