patch 8.2.2536: Coverity complains about unchecked return value

Problem:    Coverity complains about unchecked return value.
Solution:   Add (void).
diff --git a/src/userfunc.c b/src/userfunc.c
index 64a8fa6..450582c 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -4020,7 +4020,7 @@
 		    && ufunc->uf_def_status == UF_TO_BE_COMPILED
 		    && (ufunc->uf_flags & FC_DEAD) == 0)
 	    {
-		compile_def_function(ufunc, FALSE, FALSE, NULL);
+		(void)compile_def_function(ufunc, FALSE, FALSE, NULL);
 
 		if (func_hashtab.ht_changed != changed)
 		{