patch 8.2.0462: previewwindow test fails on some systems

Problem:    Previewwindow test fails on some systems. (James McCoy)
Solution:   Wait a bit after sending the "o". (closes #5849)

src/testdir/dumps/Test_popup_and_previewwindow_01.dump

@@ -16,5 +16,5 @@
 |a+0#0000001#ffd7ff255|b|6| @11| +0#0000000#a8a8a8255| +0&#ffffff0@58
 |a|b|0> @71
 |~+0#4040ff13&| @73
-|[+3#0000000&|N|o| |N|a|m|e|]| |[|+|]| @43|1|0|,|1| @10|B|o|t
+|[+3#0000000&|N|o| |N|a|m|e|]| |[|+|]| @43|1@1|,|1| @10|B|o|t
 |-+2&&@1| |K|e|y|w|o|r|d| |L|o|c|a|l| |c|o|m|p|l|e|t|i|o|n| |(|^|N|^|P|)| |m+0#00e0003&|a|t|c|h| |1| |o|f| |1|0| +0#0000000&@26

src/testdir/test_popup.vim

@@ -743,15 +743,19 @@ func Test_popup_and_previewwindow_dump()
   let lines =<< trim END
     set previewheight=9
     silent! pedit
-    call setline(1, map(repeat(["ab"], 10), "v:val. v:key"))
+    call setline(1, map(repeat(["ab"], 10), "v:val .. v:key"))
     exec "norm! G\<C-E>\<C-E>"
   END
   call writefile(lines, 'Xscript')
   let buf = RunVimInTerminal('-S Xscript', {})
 
+  " wait for the script to finish
+  call term_wait(buf)
+
   " Test that popup and previewwindow do not overlap.
-  call term_sendkeys(buf, "o\<C-X>\<C-N>")
-  sleep 100m
+  call term_sendkeys(buf, "o")
+  call term_wait(buf, 100)
+  call term_sendkeys(buf, "\<C-X>\<C-N>")
   call VerifyScreenDump(buf, 'Test_popup_and_previewwindow_01', {})
 
   call term_sendkeys(buf, "\<Esc>u")

src/version.c

@@ -738,6 +738,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    462,
 /**/
     461,
 /**/