fix: replace bare except with except Exception in image validation functions

[Suraj Kumar (surajthedev)]

Fixes #707

Description

This PR replaces bare except: clauses with except Exception: in image
validation functions, following Python best practices (PEP 8).

Changes

Replaced bare except: with except Exception: in:

• lessons/4-ComputerVision/07-ConvNets/tfcv.py
• lessons/4-ComputerVision/07-ConvNets/pytorchcv.py
• lessons/4-ComputerVision/08-TransferLearning/tfcv.py
• lessons/4-ComputerVision/08-TransferLearning/pytorchcv.py

Motivation

Bare except: clauses catch all exceptions, including SystemExit and
KeyboardInterrupt, which can mask serious errors and prevent users from
stopping the program (e.g., via Ctrl+C). Using except Exception: follows
PEP 8 guidelines and prevents masking of critical system exceptions, while
still catching all legitimate errors like corrupt or invalid image files.

Testing

• Verified syntax correctness with python -m py_compile
• Maintains the same error handling behavior for legitimate exceptions
• Allows system-level exceptions (KeyboardInterrupt, SystemExit) to
  propagate properly

[Suraj Kumar (surajthedev)]

@microsoft-github-policy-service agree

[Suraj Kumar (surajthedev)]

Hi Microsoft (@microsoft), just wanted to kindly follow up on this PR. It has been open for around 2 weeks, and I believe all the requested changes have been completed.
Whenever you get a chance, could you please take a look and let me know if any further changes are needed from my side?
Thank you for your time!