patch 9.1.0140: cursor on wrong row after 1 char 'below' virtual text when EOL is shown

Problem:  The cursor screen row was incorrectly being calculated when the
          cursor follows a 1 character text_align 'below' virtual text line,
          resulting in the cursor being shown on the wrong line.
          This was caused by a cell size of 2 instead of 1 being used for the EOL
          character, which propagated to the calculation of space for putting the
          'below' virtual text on its own line. (rickhowe)
Solution: Fix the size used for the EOL character in calculating the
          cursor's screen position (Dylan Thacker-Smith)

fixes: #11959
related: #12028
closes: #14096

Signed-off-by: Dylan Thacker-Smith <dylan.ah.smith@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_textprop.vim b/src/testdir/test_textprop.vim
index 18ff3df..7542c08 100644
--- a/src/testdir/test_textprop.vim
+++ b/src/testdir/test_textprop.vim
@@ -3075,8 +3075,9 @@
       let vt = 'test'
       call prop_type_add(vt, {'highlight': 'ToDo'})
       for ln in range(1, line('$'))
-        call prop_add(ln, 0, {'type': vt, 'text': '---', 'text_align': 'above'})
-        call prop_add(ln, 0, {'type': vt, 'text': '+++', 'text_align': 'below'})
+        " use 1 character text to test for off-by-one regressions
+        call prop_add(ln, 0, {'type': vt, 'text': '-', 'text_align': 'above'})
+        call prop_add(ln, 0, {'type': vt, 'text': '+', 'text_align': 'below'})
       endfor
       normal G
   END