patch 8.1.1421: drawing "~" line in popup window

Problem:    Drawing "~" line in popup window.
Solution:   Just draw text in the last line of the popup window.
diff --git a/src/testdir/dumps/Test_popupwin_05.dump b/src/testdir/dumps/Test_popupwin_05.dump
index bfb50f0..2c74d74 100644
--- a/src/testdir/dumps/Test_popupwin_05.dump
+++ b/src/testdir/dumps/Test_popupwin_05.dump
@@ -3,7 +3,7 @@
 |~| @73
 |~| @6|o+0#0000001#ffd7ff255|t|h|e|r| |t|a|b| @5| +0#4040ff13#ffffff0@51
 |~| @6|a+0#0000001#ffd7ff255| |c+0#ff404010&|o|m@1|e|n|t| +0#0000001&|l|i|n|e| | +0#4040ff13#ffffff0@51
-|~| @6|~+0&#ffd7ff255| @13| +0&#ffffff0@51
+|~| @6| +0&#ffd7ff255@14| +0&#ffffff0@51
 |~| @73
 |~| @73
 |~| @73
diff --git a/src/testdir/dumps/Test_popupwin_06.dump b/src/testdir/dumps/Test_popupwin_06.dump
new file mode 100644
index 0000000..3dfcbc2
--- /dev/null
+++ b/src/testdir/dumps/Test_popupwin_06.dump
@@ -0,0 +1,10 @@
+> +0&#ffffff0@74
+|~+0#4040ff13&| @73
+|~| @73
+|~| @6|o+0#0000001#ffd7ff255|t|h|e|r| |t|a|b| @15| +0#4040ff13#ffffff0@41
+|~| @6|a+0#0000001#ffd7ff255| |c+0#ff404010&|o|m@1|e|n|t| +0#0000001&|l|i|n|e| @10| +0#4040ff13#ffffff0@41
+|~| @6|t+0#0000001#ffd7ff255|h|i|s| |l|i|n|e| |w|i|l@1| |n|o|t| |f|i|t| |h|e| +0#4040ff13#ffffff0@41
+|~| @73
+|~| @73
+|~| @73
+|:+0#0000000&|r|e|d|r|a|w| @49|0|,|0|-|1| @8|A|l@1| 
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index a2d2e80..4511cd1 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -41,11 +41,16 @@
   call term_sendkeys(buf, ":quit!\<CR>")
   call VerifyScreenDump(buf, 'Test_popupwin_04', {})
 
-  " resize popup
+  " resize popup, show empty line at bottom
   call term_sendkeys(buf, ":call popup_move(popupwin, {'minwidth': 15, 'maxwidth': 25, 'minheight': 3, 'maxheight': 5})\<CR>")
   call term_sendkeys(buf, ":redraw\<CR>")
   call VerifyScreenDump(buf, 'Test_popupwin_05', {})
 
+  " show not fitting line at bottom
+  call term_sendkeys(buf, ":call setbufline(winbufnr(popupwin), 3, 'this line will not fit here')\<CR>")
+  call term_sendkeys(buf, ":redraw\<CR>")
+  call VerifyScreenDump(buf, 'Test_popupwin_06', {})
+
   " clean up
   call StopVimInTerminal(buf)
   call delete('XtestPopup')