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/globals.h b/src/globals.h
index 5495eac..5bdbad6 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -221,7 +221,6 @@
 EXTERN int	emsg_severe INIT(= FALSE);  // use message of next of several
 					    // emsg() calls for throw
 // used by assert_fails()
-EXTERN int	emsg_assert_fails_used INIT(= FALSE);
 EXTERN char_u	*emsg_assert_fails_msg INIT(= NULL);
 EXTERN long	emsg_assert_fails_lnum INIT(= 0);
 EXTERN char_u	*emsg_assert_fails_context INIT(= NULL);
@@ -1130,6 +1129,8 @@
 EXTERN int	emsg_noredir INIT(= 0);	// don't redirect error messages
 EXTERN int	cmd_silent INIT(= FALSE); // don't echo the command line
 
+EXTERN int	in_assert_fails INIT(= FALSE);	// assert_fails() active
+
 EXTERN int	swap_exists_action INIT(= SEA_NONE);
 					// For dialog when swap file already
 					// exists.