tree schema BUGFIX existing module is not a parsing error

Fixes #1656
diff --git a/src/tree_schema.c b/src/tree_schema.c
index b405ff7..cbd2e64 100644
--- a/src/tree_schema.c
+++ b/src/tree_schema.c
@@ -1595,7 +1595,7 @@
     /* success */
 
 cleanup:
-    if (ret) {
+    if (ret && (ret != LY_EEXIST)) {
         if (mod && mod->name) {
             /* there are cases when path is not available for parsing error, so this additional
              * message tries to add information about the module where the error occurred */