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/term.c b/src/term.c
index be6d531..4d4cc58 100644
--- a/src/term.c
+++ b/src/term.c
@@ -1800,7 +1800,7 @@
     mch_errmsg(_("defaulting to '"));
     mch_errmsg((char *)term);
     mch_errmsg("'\r\n");
-    if (emsg_silent == 0)
+    if (emsg_silent == 0 && !in_assert_fails)
     {
 	screen_start();	// don't know where cursor is now
 	out_flush();