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/vim9execute.c b/src/vim9execute.c
index c428a3d..09eb6c2 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -582,7 +582,7 @@
     funcexe_T   funcexe;
     int		error;
     int		idx;
-    int		called_emsg_before = called_emsg;
+    int		did_emsg_before = did_emsg;
 
     if (ufunc->uf_def_status == UF_TO_BE_COMPILED
 	    && compile_def_function(ufunc, FALSE, NULL) == FAIL)
@@ -620,7 +620,7 @@
 	user_func_error(error, ufunc->uf_name);
 	return FAIL;
     }
-    if (called_emsg > called_emsg_before)
+    if (did_emsg > did_emsg_before)
 	// Error other than from calling the function itself.
 	return FAIL;
     return OK;