patch 8.0.0858: can exit while a terminal is still running a job

Problem:    Can exit while a terminal is still running a job.
Solution:   Consider a buffer with a running job like a changed file.
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index 3f5e268..98bc758 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -63,7 +63,8 @@
 
 func Test_terminal_wipe_buffer()
   let buf = Run_shell_in_terminal()
-  exe buf . 'bwipe'
+  call assert_fails(buf . 'bwipe', 'E517')
+  exe buf . 'bwipe!'
   call WaitFor('job_status(g:job) == "dead"')
   call assert_equal('dead', job_status(g:job))
   call assert_equal("", bufname(buf))