patch 8.0.0859: NULL pointer access when term_free_vterm called twice

Problem:    NULL pointer access when term_free_vterm called twice.
Solution:   Return when tl_vterm is NULL. (Yasuhiro Matsumoto, closes #1934)

Author: brammool

src/terminal.c

@@ -691,8 +691,11 @@ move_terminal_to_buffer(term_T *term)
     VTermPos	    pos;
     VTermScreenCell cell;
     VTermScreenCell *p;
-    VTermScreen	    *screen = vterm_obtain_screen(term->tl_vterm);
+    VTermScreen	    *screen;
 
+    if (term->tl_vterm == NULL)
+	return;
+    screen = vterm_obtain_screen(term->tl_vterm);
     for (pos.row = 0; pos.row < term->tl_rows; ++pos.row)
     {
 	len = 0;

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    859,
 /**/
     858,
 /**/