vim-patch:8.2.3946: when an internal error makes Vim exit the error is not seen

Problem:    When an internal error makes Vim exit the error is not seen.
Solution:   Add the error to the test output.
1c67f3a977

Add emsg_not_now() check to make code equivalent.

src/nvim/message.c

@@ -830,8 +830,13 @@ static bool semsgv(const char *fmt, va_list ap)
 /// detected when fuzzing vim.
 void iemsg(const char *s)
 {
+  if (emsg_not_now()) {
+    return;
+  }
+
   emsg(s);
 #ifdef ABORT_ON_INTERNAL_ERROR
+  set_vim_var_string(VV_ERRMSG, s, -1);
   abort();
 #endif
 }