patch 8.2.3074: popup_atcursor() uses wrong position with concealing

Problem:    popup_atcursor() uses wrong position with concealing.
Solution:   Keep w_wcol in conceal_check_cursor_line(). (closes #8476)
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index 68d7db8..cdfa3a9 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -1462,6 +1462,13 @@
 	      \ moved: range(3),
 	      \ mousemoved: range(3),
 	      \ })
+
+	normal 9G27|Rconcealed  X
+	syn match Hidden /concealed/ conceal
+	set conceallevel=2 concealcursor=n
+	redraw
+	normal 0fX
+	call popup_atcursor('mark', {})
   END
   call writefile(lines, 'XtestPopupAtcursorPos')
   let buf = RunVimInTerminal('-S XtestPopupAtcursorPos', #{rows: 12})