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/undo.c b/src/undo.c
index 6ab8572..b913841 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -3522,21 +3522,18 @@
     int
 bufIsChanged(buf_T *buf)
 {
-    return
-#ifdef FEAT_QUICKFIX
-	    !bt_dontwrite(buf) &&
+#ifdef FEAT_TERMINAL
+    if (term_job_running(buf->b_term))
+	return TRUE;
 #endif
-	    (buf->b_changed || file_ff_differs(buf, TRUE));
+    return !bt_dontwrite(buf)
+	&& (buf->b_changed || file_ff_differs(buf, TRUE));
 }
 
     int
 curbufIsChanged(void)
 {
-    return
-#ifdef FEAT_QUICKFIX
-	!bt_dontwrite(curbuf) &&
-#endif
-	(curbuf->b_changed || file_ff_differs(curbuf, TRUE));
+    return bufIsChanged(curbuf);
 }
 
 #if defined(FEAT_EVAL) || defined(PROTO)