don't offer subcommands after a dash option

docs/examples/core/ipython-completion.bash

@@ -30,6 +30,10 b' _ipython()'
         [ "$cur" = "$i" ] && break
         if [[ ${subcommands} == *${i}* ]]; then
             mode="$i"
+            break
+        elif [[ ${i} == "--"* ]]; then
+            mode="nosubcommand"
+            break
         fi
     done