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/gui.c b/src/gui.c
index 7b61381..41647d6 100644
--- a/src/gui.c
+++ b/src/gui.c
@@ -4906,6 +4906,9 @@
 
     row = Y_2_ROW(y);
     col = X_2_COL(x);
+
+    col -= TPL_LCOL(NULL);
+
     if (row < 0 || col < 0)		// before first window
 	return NULL;
     wp = mouse_find_win(&row, &col, popup);
@@ -5376,6 +5379,8 @@
     int		col = X_2_COL(x);
     win_T	*wp;
 
+    col -= TPL_LCOL(NULL);
+
     if (row < 0 || col < 0)
 	return;