patch 8.1.2295: if buffer of popup is in another window cursorline sign shows

Problem:    If buffer of popup is in another window cursorline sign shows.
Solution:   Check the group of the sign.
diff --git a/src/screen.c b/src/screen.c
index 0120d11..8453c8d 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -4615,7 +4615,7 @@
 # ifdef FEAT_SIGNS
     // If 'signcolumn' is set to 'number' and there is a sign to display, then
     // the minimal width for the number column is 2.
-    if (n < 2 && (wp->w_buffer->b_signlist != NULL)
+    if (n < 2 && get_first_valid_sign(wp) != NULL
 	    && (*wp->w_p_scl == 'n' && *(wp->w_p_scl + 1) == 'u'))
 	n = 2;
 # endif