fix(pum): position properly with ext_multigrid

(cherry picked from commit 239d19d908)

test/functional/ui/mouse_spec.lua

@@ -1849,5 +1849,17 @@ describe('ui/mouse/input', function()
     feed('<Down><CR>')
     eq(2, funcs.winnr())
     eq('', funcs.getreg('"'))
+
+    -- Test for right click in visual mode inside the selection with vertical splits
+    command('wincmd t')
+    command('rightbelow vsplit')
+    funcs.setreg('"', '')
+    meths.win_set_cursor(0, {1, 9})
+    feed('vee')
+    meths.input_mouse('right', 'press', '', 0, 0, 52)
+    meths.input_mouse('right', 'release', '', 0, 0, 52)
+    feed('<Down><CR>')
+    eq({1, 9}, meths.win_get_cursor(0))
+    eq('ran away', funcs.getreg('"'))
   end)
 end)