patch 8.0.0853: crash when running terminal with unknown command

Problem:    Crash when running terminal with unknown command.
Solution:   Check "term" not to be NULL. (Yasuhiro Matsumoto, closes #1932)
diff --git a/src/terminal.c b/src/terminal.c
index abdb50b..b06feff 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -629,7 +629,8 @@
 {
     /* Also consider the job finished when the channel is closed, to avoid a
      * race condition when updating the title. */
-    return term->tl_job != NULL
+    return term != NULL
+	&& term->tl_job != NULL
 	&& term->tl_job->jv_status == JOB_STARTED
 	&& channel_is_open(term->tl_job->jv_channel);
 }