Fixed Rex Scheduler Warm Up (axolotl-ai-cloud#2535) [skip ci]

* Fixed Rex Scheduler Warm Up

* chore: lint

---------

Co-authored-by: Wing Lian <[email protected]>

Author: Catgat

src/axolotl/utils/schedulers.py

@@ -40,7 +40,7 @@ def __init__(
         self.max_lr = max_lr
         self.total_steps = total_steps
         self.num_warmup_steps = num_warmup_steps
-        self.last_step = last_step - 1
+        self.last_step = max(last_step - 1, 0)
 
         # Ensure each parameter group has an "initial_lr" key to avoid issues when resuming.
         for group in optimizer.param_groups: