patch 9.0.0143: cursor positioned after virtual text in empty line

Problem:    Cursor positioned after virtual text in empty line.
Solution:   Keep cursor in the first column. (closes #10786)
diff --git a/src/charset.c b/src/charset.c
index c32044a..f7ce335 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -1127,7 +1127,7 @@
     size = win_chartabsize(wp, s, vcol);
 
 # ifdef FEAT_PROP_POPUP
-    if (cts->cts_has_prop_with_text)
+    if (cts->cts_has_prop_with_text && *line != NUL)
     {
 	int	    i;
 	int	    col = (int)(s - line);