fix tab context menu close (invalid switching after deletion)

src/xschem.tcl

@@ -5604,11 +5604,15 @@ proc tab_ctx_cmd {tab_but what} {
       xschem new_schematic switch $old {} 0 ;# no draw
     } elseif {$what eq {close}} {
       set old [xschem get current_win_path]
+      set ntabs [xschem get ntabs]
       xschem new_schematic switch $win_path {} 0 ;# no draw
-      xschem exit
+      set remaining_tabs [xschem exit]
+      if { $old != $win_path || $remaining_tabs == $ntabs} {
+        # don't switch if we were on the tab that has been closed.
         xschem new_schematic switch $old {} 1 ;# draw
       }
     }
+  }
   # puts $filename
 }
 proc tab_context_menu {tab_but} {