Fix nested manual cast

[KohakuBlueleaf]

Description

Avoid error in this situation:

with manual_cast():
  with manual_cast():
    pass

Which will be triggered by hires-fix.

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests

[AUTOMATIC1111]

Wouldn't that disable it too early?

# disabled
with manual_cast():
  # enabed
  with manual_cast():
    # enabed
    pass
   # disabled  <--- should be enabled here
#disabled

[KohakuBlueleaf]

@AUTOMATIC1111 Fixed