patch 8.0.0159: crash on startup when updating tabline

Problem:    Using a NULL pointer when using feedkeys() to trigger drawing a
            tabline.
Solution:   Skip drawing a tabline if TabPageIdxs is NULL. (Dominique Pelle)
            Also fix recursing into getcmdline() from the cmd window.

src/ex_getln.c

@@ -772,7 +772,9 @@ getcmdline(
 		/*
 		 * Open a window to edit the command line (and history).
 		 */
+		save_cmdline(&save_ccline);
 		c = ex_window();
+		restore_cmdline(&save_ccline);
 		some_key_typed = TRUE;
 	    }
 	}

src/screen.c

@@ -3650,7 +3650,7 @@ win_line(
 		if (fdc > 0)
 		{
 		    /* Draw the 'foldcolumn'.  Allocate a buffer, "extra" may
-		     * already be in used. */
+		     * already be in use. */
 		    p_extra_free = alloc(12 + 1);
 
 		    if (p_extra_free != NULL)
@@ -10344,6 +10344,8 @@ draw_tabline(void)
 #endif
 					    );
 
+    if (ScreenLines == NULL)
+	return;
     redraw_tabline = FALSE;
 
 #ifdef FEAT_GUI_TABLINE

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    159,
 /**/
     158,
 /**/