patch 8.2.0137: crash when using win_execute() from a new tab

Problem:    Crash when using win_execute() from a new tab.
Solution:   Set the tp_*win pointers. (Ozaki Kiichi, closes #5512)
diff --git a/src/window.c b/src/window.c
index 1096b60..0c3c7f6 100644
--- a/src/window.c
+++ b/src/window.c
@@ -3616,6 +3616,9 @@
 	return FAIL;
     first_tabpage->tp_topframe = topframe;
     curtab = first_tabpage;
+    curtab->tp_firstwin = firstwin;
+    curtab->tp_lastwin = lastwin;
+    curtab->tp_curwin = curwin;
 
     return OK;
 }
@@ -3854,6 +3857,8 @@
 	    newtp->tp_next = tp->tp_next;
 	    tp->tp_next = newtp;
 	}
+	newtp->tp_firstwin = newtp->tp_lastwin = newtp->tp_curwin = curwin;
+
 	win_init_size();
 	firstwin->w_winrow = tabline_height();
 	win_comp_scroll(curwin);