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/fileio.c b/src/fileio.c
index 9eecb01..27e9aae 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4208,7 +4208,7 @@
 			msg_puts_attr(mesg2, HL_ATTR(HLF_W) + MSG_HIST);
 		    msg_clr_eos();
 		    (void)msg_end();
-		    if (emsg_silent == 0)
+		    if (emsg_silent == 0 && !in_assert_fails)
 		    {
 			out_flush();
 #ifdef FEAT_GUI