patch 8.2.0523: loops are repeated

Problem:    Loops are repeated.
Solution:   Use FOR_ALL_ macros. (Yegappan Lakshmanan, closes #5882)
diff --git a/src/popupwin.c b/src/popupwin.c
index 608db4c..863439e 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -2133,7 +2133,7 @@
 	// - another popup window with a terminal
 	// - the previous window
 	// - the first one.
-	for (owp = first_popupwin; owp != NULL; owp = owp->w_next)
+	FOR_ALL_POPUPWINS(owp)
 	    if (owp != curwin && owp->w_buffer->b_term != NULL)
 		break;
 	if (owp != NULL)