patch 9.1.1296: completion: incorrect truncation logic

Problem:  completion: incorrect truncation logic (after: v9.1.1284)
Solution: replace string allocation with direct screen rendering and
          fixe RTL/LTR truncation calculations (glepnir)

closes: #17081

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/structs.h b/src/structs.h
index 9b44598..b5c898d 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -3851,6 +3851,7 @@
     int	eob;
     int	lastline;
     int trunc;
+    int truncrl;
 } fill_chars_T;
 
 /*