Potential fix for code scanning alert no. 57: Uncontrolled data used in path expression

[praveenkk123]

Potential fix for https://github.com/intel/AI-PC-Samples/security/code-scanning/57

To fix this issue, we should validate user-provided folder paths before using them for file system operations. The most appropriate fix is to constrain the user's input to a directory under a known root (project subdirectory), and check that the path, after normalization (using os.path.abspath or os.path.normpath), remains under that root. Concretely,

• Define a safe root directory for all video datasets (e.g., a constant like DATASET_ROOT = "./datasets").
• When receiving the folder name from the user, join it to the root and normalize/absolutize the resulting path.
• Before calling os.walk, check that this normalized path starts with the root directory's absolute path.
• If validation fails, raise an informative error or warn the user, and do not proceed.
  This prevents traversal attacks or access to arbitrary directories.

Specific changes:

• Add a DATASET_ROOT constant, pointing to a known safe directory (e.g., ./datasets).
• In get_video_paths, join DATASET_ROOT with the user-specified folder, normalize, and check containment.
• Add an import for any needed utilities if not already present (only standard library).
• Display errors via Streamlit if folder validation fails.

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