UI: fix cursor not displayed after hiding and un-hiding #12811

- TUI: Fix a case where the cursor was not displayed after hiding the
  cursor and then setting it to be displayed again.
- Change to reset everything before setting guicursor.

fixes #12800
close #12811

Steps to reproduce:

    nvim -u NORC
    :set termguicolors
    :hi nCursor guifg=red guibg=red
    :hi iCursor guifg=green guibg=green
    :hi cCursor guifg=blue guibg=blue
    :set guicursor=n:block-nCursor,i:hor25-iCursor,c:ver25-cCursor
    :set guicursor-=c:ver25-cCursor

Actual behaviour: Cursor is a blue vertical.
Expected behaviour: Cursor should be the default color block.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/nvim/tui/tui.c b/src/nvim/tui/tui.c
index dde17726fd..2ef9bf5a2e 100644
--- a/src/nvim/tui/tui.c
+++ b/src/nvim/tui/tui.c
@@ -1083,6 +1083,7 @@ static void tui_set_mode(UI *ui, ModeShape mode)
     }
   } else if (c.id == 0) {
     // No cursor color for this mode; reset to default.
+    data->want_invisible = false;
     unibi_out_ext(ui, data->unibi_ext.reset_cursor_color);
   }