Scheduler Variable UnboundLocalError for DDIM and DPM Solver

[shorty07]

Bug Description: ACE-Step fails with UnboundLocalError: cannot access local variable 'scheduler' where it is not associated with a value when using DDIM or DPM solver scheduler types. Only Euler scheduler works correctly.

UnboundLocalError: cannot access local variable 'scheduler' where it is not associated with a value

Root Cause : In pipeline_ace_step.py around line 900-950, the scheduler selection logic has incomplete implementation:

Euler scheduler : Properly initializes scheduler variable

DDIM/DPM schedulers : Have conditional branches but the scheduler variable is never assigned

Later usage : Code tries to reference uninitialized scheduler variable

Reproduction Steps
Initialize ACEStepPipeline

Call model with scheduler_type="ddim" or scheduler_type="dpm-solver"

Error occurs in text2music_diffusion_process method

Working Configuration
model(
scheduler_type="euler", # Works
# ... other parameters
)

Failing Configurations
model(
scheduler_type="ddim", # Fails
scheduler_type="dpm-solver", # Fails
# ... other parameters
)

Impact: High : Breaks core functionality for 2 out of 3 documented scheduler types

Regression : Likely introduced in recent refactoring of scheduler initialization code