patch 8.1.0577: tabpage right-click menu never shows "Close tab"

Problem:    Tabpage right-click menu never shows "Close tab".
Solution:   Always create the "Close tab" item but ignore the event if there
            is only one tab.
diff --git a/src/gui.c b/src/gui.c
index 2f3bafc..9160848 100644
--- a/src/gui.c
+++ b/src/gui.c
@@ -3865,10 +3865,14 @@
 {
     char_u	    string[3];
 
-    /* Don't put events in the input queue now. */
+    // Don't put events in the input queue now.
     if (hold_gui_events)
 	return;
 
+    // Cannot close the last tabpage.
+    if (event == TABLINE_MENU_CLOSE && first_tabpage->tp_next == NULL)
+	return;
+
     string[0] = CSI;
     string[1] = KS_TABMENU;
     string[2] = KE_FILLER;
diff --git a/src/gui_gtk_x11.c b/src/gui_gtk_x11.c
index dbddb0f..898e2af 100644
--- a/src/gui_gtk_x11.c
+++ b/src/gui_gtk_x11.c
@@ -3337,9 +3337,7 @@
     GtkWidget *menu;
 
     menu = gtk_menu_new();
-    if (first_tabpage->tp_next != NULL)
-	add_tabline_menu_item(menu, (char_u *)_("Close tab"),
-							  TABLINE_MENU_CLOSE);
+    add_tabline_menu_item(menu, (char_u *)_("Close tab"), TABLINE_MENU_CLOSE);
     add_tabline_menu_item(menu, (char_u *)_("New tab"), TABLINE_MENU_NEW);
     add_tabline_menu_item(menu, (char_u *)_("Open Tab..."), TABLINE_MENU_OPEN);
 
diff --git a/src/gui_mac.c b/src/gui_mac.c
index 96f04c5..ec8ec3a 100644
--- a/src/gui_mac.c
+++ b/src/gui_mac.c
@@ -6705,8 +6705,7 @@
 
     // create tabline popup menu required by vim docs (see :he tabline-menu)
     CreateNewMenu(kTabContextMenuId, 0, &contextMenu);
-    if (first_tabpage->tp_next != NULL)
-	AppendMenuItemTextWithCFString(contextMenu, CFSTR("Close Tab"), 0,
+    AppendMenuItemTextWithCFString(contextMenu, CFSTR("Close Tab"), 0,
 						    TABLINE_MENU_CLOSE, NULL);
     AppendMenuItemTextWithCFString(contextMenu, CFSTR("New Tab"), 0,
 						      TABLINE_MENU_NEW, NULL);
diff --git a/src/gui_motif.c b/src/gui_motif.c
index 8467c52..b6c140b 100644
--- a/src/gui_motif.c
+++ b/src/gui_motif.c
@@ -514,21 +514,18 @@
     XtVaSetValues(scroller, XmNwidth, 0, XmNresizable, False,
 		  XmNtraversalOn, False, NULL);
 
-    /* Create the tabline popup menu */
+    // Create the tabline popup menu
     tabLine_menu = XmCreatePopupMenu(tabLine, "tabline popup", NULL, 0);
 
-    /* Add the buttons to the menu */
-    if (first_tabpage->tp_next != NULL)
-    {
-	n = 0;
-	XtSetArg(args[n], XmNuserData, TABLINE_MENU_CLOSE); n++;
-	xms = XmStringCreate((char *)"Close tab", STRING_TAG);
-	XtSetArg(args[n], XmNlabelString, xms); n++;
-	button = XmCreatePushButton(tabLine_menu, "Close", args, n);
-	XtAddCallback(button, XmNactivateCallback,
-		      (XtCallbackProc)tabline_button_cb, NULL);
-	XmStringFree(xms);
-    }
+    // Add the buttons to the tabline popup menu
+    n = 0;
+    XtSetArg(args[n], XmNuserData, TABLINE_MENU_CLOSE); n++;
+    xms = XmStringCreate((char *)"Close tab", STRING_TAG);
+    XtSetArg(args[n], XmNlabelString, xms); n++;
+    button = XmCreatePushButton(tabLine_menu, "Close", args, n);
+    XtAddCallback(button, XmNactivateCallback,
+		  (XtCallbackProc)tabline_button_cb, NULL);
+    XmStringFree(xms);
 
     n = 0;
     XtSetArg(args[n], XmNuserData, TABLINE_MENU_NEW); n++;
diff --git a/src/version.c b/src/version.c
index 29fdfb2..0600217 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    577,
+/**/
     576,
 /**/
     575,