patch 9.1.1391: Vim does not have a vertical tabpanel

Problem:  Vim does not have a tabpanel
Solution: include the tabpanel feature
          (Naruhiko Nishino, thinca)

closes: #17263

Co-authored-by: thinca <thinca@gmail.com>
Signed-off-by: Naruhiko Nishino <naru123456789@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/structs.h b/src/structs.h
index 1cb70b8..cd7370d 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -3851,6 +3851,9 @@
     int	diff;
     int	eob;
     int	lastline;
+#if defined(FEAT_TABPANEL)
+    int	tpl_vert;
+#endif
     int trunc;
     int truncrl;
 } fill_chars_T;