patch 8.1.1403: cannot build without the timer feature

Problem:    Cannot build without the timer feature.
Solution:   Add #ifdef.
diff --git a/src/popupwin.c b/src/popupwin.c
index f08f784..116efcb 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -30,6 +30,7 @@
     wp->w_wincol = dict_get_number(dict, (char_u *)"col");
     wp->w_zindex = dict_get_number(dict, (char_u *)"zindex");
 
+#if defined(FEAT_TIMERS)
     // Add timer to close the popup after some time.
     nr = dict_get_number(dict, (char_u *)"time");
     if (nr > 0)
@@ -49,6 +50,7 @@
 	    wp->w_popup_timer->tr_partial = tv.vval.v_partial;
 	}
     }
+#endif
 
 }