patch 8.0.1317: accessing freed memory in term_wait()

Problem:    Accessing freed memory in term_wait(). (Dominique Pelle)
Solution:   Check that the buffer still exists.

src/terminal.c

@@ -3227,6 +3227,10 @@ f_term_wait(typval_T *argvars, typval_T *rettv UNUSED)
 	{
 	    mch_check_messages();
 	    parse_queued_messages();
+	    if (!buf_valid(buf))
+		/* If the terminal is closed when the channel is closed the
+		 * buffer disappears. */
+		break;
 	    ui_delay(10L, FALSE);
 	}
 	mch_check_messages();

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1317,
 /**/
     1316,
 /**/