handle EndRegion as no-op

src/step.rs

@@ -141,6 +141,8 @@ fn statement(&mut self, stmt: &mir::Statement<'tcx>) -> EvalResult<'tcx> {
                 self.deallocate_local(old_val)?;
             }
 
+            EndRegion(..) => {}
+
             // Defined to do nothing. These are added by optimization passes, to avoid changing the
             // size of MIR constantly.
             Nop => {}