patch 9.1.0447: completion may be wrong when deleting all chars

Problem:  completion may be wrong when deleting all chars
Solution: reset compl_shown_match

closes: #14854

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/insexpand.c b/src/insexpand.c
index c420c0e..c1374d3 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -1255,6 +1255,12 @@
     if (match_at_original_text(compl_shown_match))
 	shown_match_ok = TRUE;
 
+    if (compl_leader != NULL
+	    && STRCMP(compl_leader, compl_orig_text) == 0
+	    && shown_match_ok == FALSE)
+	compl_shown_match = compl_no_select ? compl_first_match
+					    : compl_first_match->cp_next;
+
     i = 0;
     compl = compl_first_match;
     do