schema compile BUGFIX dev node copy double free in extensions

Fixes #1621
diff --git a/src/schema_compile_amend.c b/src/schema_compile_amend.c
index 0cb0c84..13e1a47 100644
--- a/src/schema_compile_amend.c
+++ b/src/schema_compile_amend.c
@@ -1508,6 +1508,8 @@
 void
 lysp_dev_node_free(const struct ly_ctx *ctx, struct lysp_node *dev_pnode)
 {
+    LY_ARRAY_COUNT_TYPE u;
+
     if (!dev_pnode) {
         return;
     }
@@ -1550,6 +1552,12 @@
         return;
     }
 
+    /* extension parsed tree and children were not duplicated */
+    LY_ARRAY_FOR(dev_pnode->exts, u) {
+        dev_pnode->exts[u].parsed = NULL;
+        dev_pnode->exts[u].child = NULL;
+    }
+
     lysp_node_free((struct ly_ctx *)ctx, dev_pnode);
 }