patch 8.1.2210: using negative offset for popup_create() does not work

Problem:    Using negative offset for popup_create() does not work.
Solution:   Use -1 instead of zero. (closes #5111)
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index dc382d8..1c5bcb2 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -278,7 +278,7 @@
 	      \ border: [],
 	      \ padding: [],
 	      \ })
-	normal 25|r@
+	normal 24|r@
 	let winid1 = popup_create(['First', 'SeconD'], #{
 	      \ line: 'cursor+1',
 	      \ col: 'cursor',
@@ -286,7 +286,7 @@
 	      \ border: [],
 	      \ padding: [],
 	      \ })
-	normal 9G29|r%
+	normal 9G27|r%
 	let winid1 = popup_create(['fiRSt', 'seCOnd'], #{
 	      \ line: 'cursor-1',
 	      \ col: 'cursor',
@@ -294,7 +294,7 @@
 	      \ border: [],
 	      \ padding: [],
 	      \ })
-	normal 51|r&
+	normal 48|r&
 	let winid1 = popup_create(['FIrsT', 'SEcoND'], #{
 	      \ line: 'cursor-1',
 	      \ col: 'cursor',
@@ -302,6 +302,14 @@
 	      \ border: [],
 	      \ padding: [],
 	      \ })
+	normal 1G51|r*
+	let winid1 = popup_create(['one', 'two'], #{
+	      \ line: 'cursor-1',
+	      \ col: 'cursor',
+	      \ pos: 'botleft',
+	      \ border: [],
+	      \ padding: [],
+	      \ })
   END
   call writefile(lines, 'XtestPopupCorners')
   let buf = RunVimInTerminal('-S XtestPopupCorners', #{rows: 12})