Fix getting sanbox resources with empty out dir

commit_hash:930104d5723ad17f67f7ed7e2d209ea5ffb4f76e

Author: nogert

build/export_generators/ide-gradle/codegen_from_sandbox.jinja

@@ -3,7 +3,7 @@
 {%-     for from_sandbox in current_target.from_sandboxes %}
 
 val {{ varprefix }}{{ from_sandbox['_object_index'] }} = tasks.register<Exec>("{{ varprefix }}{{ from_sandbox['_object_index'] }}") {
-    workingDir(layout.buildDirectory.dir("{%- if from_sandbox.reldir != "." -%}/{{ from_sandbox.reldir }}{%- endif -%}"))
+    workingDir(layout.buildDirectory{%- if from_sandbox.reldir != "." -%}.dir("/{{ from_sandbox.reldir }}"){%- endif -%})
     commandLine("bash", "-c", listOf(
         "{{ arcadia_root }}/ya",
         "download",