patch 8.2.0011: screen updating wrong when opeing preview window

Problem:    Screen updating wrong when opeing preview window.
Solution:   Redraw the window when the preview window opens.

src/popupmenu.c

@@ -913,7 +913,7 @@ pum_set_selected(int n, int repeat UNUSED)
 			// When the preview window was resized we need to
 			// update the view on the buffer.  Only go back to
 			// the window when needed, otherwise it will always be
-			// redraw.
+			// redrawn.
 			if (resized && win_valid(curwin_save))
 			{
 			    ++no_u_sync;
@@ -926,8 +926,9 @@ pum_set_selected(int n, int repeat UNUSED)
 			// Enable updating the status lines.
 			pum_pretend_not_visible = TRUE;
 			// But don't draw text at the new popup menu position,
-			// it causes flicker.
+			// it causes flicker.  When resizing we need to draw
-			pum_will_redraw = TRUE;
+			// anyway, the position may change later.
+			pum_will_redraw = !resized;
 			update_screen(0);
 			pum_pretend_not_visible = FALSE;
 			pum_will_redraw = FALSE;
@@ -949,7 +950,7 @@ pum_set_selected(int n, int repeat UNUSED)
 			// May need to update the screen again when there are
 			// autocommands involved.
 			pum_pretend_not_visible = TRUE;
-			pum_will_redraw = TRUE;
+			pum_will_redraw = !resized;
 			update_screen(0);
 			pum_pretend_not_visible = FALSE;
 			pum_will_redraw = FALSE;

src/testdir/dumps/Test_pum_with_preview_win.dump

@@ -0,0 +1,12 @@
+|1+0&#ffffff0|i|n|f|o| @69
+|~+0#4040ff13&| @73
+|~| @73
+|[+1#0000000&|S|c|r|a|t|c|h|]| |[|P|r|e|v|i|e|w|]| @37|1|,|1| @11|A|l@1
+|o+0&&|n|e> @71
+|o+0#0000001#e0e0e08|n|e| @11| +0#4040ff13#ffffff0@59
+|t+0#0000001#ffd7ff255|w|o| @11| +0#4040ff13#ffffff0@59
+|t+0#0000001#ffd7ff255|h|r|e@1| @9| +0#4040ff13#ffffff0@59
+|~| @73
+|~| @73
+|[+3#0000000&|N|o| |N|a|m|e|]| |[|+|]| @43|1|,|1| @11|A|l@1
+|-+2&&@1| |O|m|n|i| |c|o|m|p|l|e|t|i|o|n| |(|^|O|^|N|^|P|)| |m+0#00e0003&|a|t|c|h| |1| |o|f| |3| +0#0000000&@34

src/testdir/test_ins_complete.vim

@@ -404,3 +404,30 @@ func Test_pum_with_folds_two_tabs()
   call StopVimInTerminal(buf)
   call delete('Xpumscript')
 endfunc
+
+func Test_pum_with_preview_win()
+  CheckScreendump
+
+  let lines =<< trim END
+      funct Omni_test(findstart, base)
+	if a:findstart
+	  return col(".") - 1
+	endif
+	return [#{word: "one", info: "1info"}, #{word: "two", info: "2info"}, #{word: "three", info: "3info"}]
+      endfunc
+      set omnifunc=Omni_test
+      set completeopt+=longest
+  END
+
+  call writefile(lines, 'Xpreviewscript')
+  let buf = RunVimInTerminal('-S Xpreviewscript', #{rows: 12})
+  call term_wait(buf, 100)
+  call term_sendkeys(buf, "Gi\<C-X>\<C-O>")
+  call term_wait(buf, 100)
+  call term_sendkeys(buf, "\<C-N>")
+  call VerifyScreenDump(buf, 'Test_pum_with_preview_win', {})
+
+  call term_sendkeys(buf, "\<Esc>")
+  call StopVimInTerminal(buf)
+  call delete('Xpreviewscript')
+endfunc

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    11,
 /**/
     10,
 /**/