patch 9.0.0134: no test for text property with column zero

Problem:    No test for text property with column zero.
Solution:   Add a test.  Add message to assert for no open popups.
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 69443c5..c7140e5 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -245,7 +245,7 @@
 
   " Check for and close any stray popup windows.
   if has('popupwin')
-    call assert_equal([], popup_list())
+    call assert_equal([], popup_list(), 'Popup is still present')
     call popup_clear(1)
   endif