patch 9.0.1305: cursor in wrong line with virtual text above

Problem:    Cursor in wrong line with virtual text above.
Solution:   Count extra line for text property above/below. (closes #11959)

src/structs.h

@@ -4781,6 +4781,7 @@ typedef struct {
     textprop_T	*cts_text_props;	// text props (allocated)
     char	cts_has_prop_with_text; // TRUE if if a property inserts text
     int		cts_cur_text_width;     // width of current inserted text
+    int		cts_prop_lines;		// nr of properties above or below
     int		cts_first_char;		// width text props above the line
     int		cts_with_trailing;	// include size of trailing props with
 					// last character