patch 9.0.0151: a "below" aligned text property does not work with 'nowrap'

Problem:    A "below" aligned text property does not work with 'nowrap'.
Solution:   Start a new screen line to display the virtual text.
            (closes #10851)
diff --git a/src/proto/textprop.pro b/src/proto/textprop.pro
index 3d2e68f..c72b0ef 100644
--- a/src/proto/textprop.pro
+++ b/src/proto/textprop.pro
@@ -4,6 +4,7 @@
 void f_prop_add_list(typval_T *argvars, typval_T *rettv);
 int prop_add_common(linenr_T start_lnum, colnr_T start_col, dict_T *dict, buf_T *default_buf, typval_T *dict_arg);
 int get_text_props(buf_T *buf, linenr_T lnum, char_u **props, int will_change);
+int prop_count_below(buf_T *buf, linenr_T lnum);
 int count_props(linenr_T lnum, int only_starting, int last_line);
 int find_visible_prop(win_T *wp, int type_id, int id, textprop_T *prop, linenr_T *found_lnum);
 void add_text_props(linenr_T lnum, textprop_T *text_props, int text_prop_count);