patch 8.2.0393: Coverity warns for not using return value

Problem:    Coverity warns for not using return value.
Solution:   Add (void).
diff --git a/src/popupmenu.c b/src/popupmenu.c
index 3a5e103..c57681c 100644
--- a/src/popupmenu.c
+++ b/src/popupmenu.c
@@ -1071,12 +1071,13 @@
 {
     if (!pum_visible())
 	return;
-    dict_add_number(dict, "height", pum_height);
-    dict_add_number(dict, "width", pum_width);
-    dict_add_number(dict, "row", pum_row);
-    dict_add_number(dict, "col", pum_col);
-    dict_add_number(dict, "size", pum_size);
-    dict_add_bool(dict, "scrollbar", pum_scrollbar ? VVAL_TRUE : VVAL_FALSE);
+    (void)dict_add_number(dict, "height", pum_height);
+    (void)dict_add_number(dict, "width", pum_width);
+    (void)dict_add_number(dict, "row", pum_row);
+    (void)dict_add_number(dict, "col", pum_col);
+    (void)dict_add_number(dict, "size", pum_size);
+    (void)dict_add_bool(dict, "scrollbar",
+				       pum_scrollbar ? VVAL_TRUE : VVAL_FALSE);
 }
 #endif