Various fixes [stage]

core/src/main/java/io/xpipe/core/process/StubShellControl.java

@@ -6,6 +6,12 @@ public class StubShellControl extends WrapperShellControl {
         super(parent);
     }
 
+    @Override
+    public ShellControl start() throws Exception {
+        super.start();
+        return this;
+    }
+
     @Override
     public boolean canHaveSubshells() {
         return parent.canHaveSubshells();