patch 8.2.1919: assert_fails() setting emsg_silent changes normal execution

Problem:    Assert_fails() setting emsg_silent changes normal execution.
Solution:   Use a separate flag in_assert_fails.
diff --git a/src/insexpand.c b/src/insexpand.c
index 87aaf7d..7e61e61 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -298,7 +298,7 @@
 	msg_attr(dict_opt ? _("'dictionary' option is empty")
 			  : _("'thesaurus' option is empty"),
 							      HL_ATTR(HLF_E));
-	if (emsg_silent == 0)
+	if (emsg_silent == 0 && !in_assert_fails)
 	{
 	    vim_beep(BO_COMPL);
 	    setcursor();