tree data UPDATE lyd_find_sibling_* must ignore opaque nodes

They cannot be returned because hash search will
never find them so there would be a functional
difference when hashes are used and when not.
diff --git a/src/xpath.c b/src/xpath.c
index 9a197ac..fcfec99 100644
--- a/src/xpath.c
+++ b/src/xpath.c
@@ -6172,6 +6172,10 @@
         } else {
             r = lyd_find_sibling_val(siblings, scnode, NULL, 0, &sub);
         }
+        if (r == LY_ENOTFOUND) {
+            /* may still be an opaque node */
+            r = lyd_find_sibling_opaq_next(siblings, scnode->name, &sub);
+        }
         LY_CHECK_ERR_GOTO(r && (r != LY_ENOTFOUND), ret = r, cleanup);
 
         /* when check */