fix: Correct NCX parsing logic - use AND instead of OR

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Problem

When reading EPUBs created by ebooklib itself with ignore_ncx=True, parsing fails with:
AttributeError: 'NoneType' object has no attribute 'get_name'

Root Cause

Line 1728 had incorrect logic using or:

if not self.options.get("ignore_ncx") or not nav_item:
With ignore_ncx=True and nav_item=None, this evaluates to False or True = True, still trying to load NCX.
Fix
Changed or to and:
if toc and not self.options.get("ignore_ncx") and not nav_item:
Now NCX is only loaded when:
- 
toc attribute exists AND
- 
ignore_ncx=False AND  
- 
nav_item=None
Testing
All 9 EPUB tests pass after fix.

[c1924959470]

   您好！您的来信我已接受，我会尽快回复您。