patch 8.2.0117: crash when using gettabwinvar() with invalid arguments

Problem:    Crash when using gettabwinvar() with invalid arguments. (Yilin
            Yang)
Solution:   Use "curtab" if "tp" is NULL. (closes #5475)

src/evalwindow.c

@@ -183,7 +183,8 @@ find_win_by_nr(
     {
 #ifdef FEAT_PROP_POPUP
 	// check tab-local popup windows
-	for (wp = tp->tp_first_popupwin; wp != NULL; wp = wp->w_next)
+	for (wp = (tp == NULL ? curtab : tp)->tp_first_popupwin;
+						   wp != NULL; wp = wp->w_next)
 	    if (wp->w_id == nr)
 		return wp;
 	// check global popup windows

src/testdir/test_getvar.vim

@@ -83,6 +83,7 @@ func Test_var()
 
   unlet def_dict
 
+  call assert_equal("", gettabwinvar(9, 2020, ''))
   call assert_equal('', gettabwinvar(2, 3, '&nux'))
   call assert_equal(1, gettabwinvar(2, 3, '&nux', 1))
   tabonly

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    117,
 /**/
     116,
 /**/