patch 8.2.4154: ml_get error when exchanging windows in Visual mode

Problem:    ml_get error when exchanging windows in Visual mode.
Solution:   Correct end of Visual area when entering another buffer.

src/testdir/test_visual.vim

@@ -1318,5 +1318,15 @@ func Test_visual_block_insert_round_off()
   bwipe!
 endfunc
 
+" this was causing an ml_get error
+func Test_visual_exchange_windows()
+  enew!
+  new
+  call setline(1, ['foo', 'bar'])
+  exe "normal G\<C-V>gg\<C-W>\<C-X>OO\<Esc>"
+  bwipe!
+  bwipe!
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4154,
 /**/
     4153,
 /**/

src/window.c

@@ -1691,6 +1691,11 @@ win_exchange(long Prenum)
 
     (void)win_comp_pos();		// recompute window positions
 
+    if (wp->w_buffer != curbuf)
+	reset_VIsual_and_resel();
+    else if (VIsual_active)
+	wp->w_cursor = curwin->w_cursor;
+
     win_enter(wp, TRUE);
     redraw_all_later(NOT_VALID);
 }