Fix wallpaper-restore.sh: safe ~ expansion, handle spaces, add robustness checks

[rajghosh06-dev]

Fix wallpaper-restore.sh: safe ~ expansion, handle spaces, add robustness checks (to ~ path)

This PR improves wallpaper-restore.sh by:

• Replacing sed-based ~ expansion with safe handling (only expands leading ~).
• Adding quotes around variables to support paths with spaces.
• Using realpath -m to normalize paths.
• Adding guards for empty cache entries, relative paths, broken symlinks, and non-image files.

Tested with (following in local machine)

• ~/Pictures/... paths → expands correctly
• /home/user/Pictures/... absolute paths → untouched
• Paths containing spaces (e.g., Holiday Photos) → handled safely
• Empty or malformed cache entries → falls back to default
• Broken symlinks → falls back to default
• Non-image files (e.g., accidentally cached .txt) → rejected, default used

This prevents corrupted paths and ensures wallpapers are restored reliably across different setups.

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Checklist for Reviewing

• Verified safe handling of ~ expansion
• Confirmed quoted variables prevent issues with spaces
• Tested normalization with realpath -m
• Checked fallback behavior for empty cache entries
• Confirmed handling of relative paths
• Validated broken symlink detection
• Ensured non-image files are rejected gracefully
• Confirmed default wallpaper is used when needed

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Before vs After

Aspect	Before (Old Script)	After (Improved Script)
~ expansion	Used sed -i (risk of corrupting folder names)	Safe expansion only at start of path
Handling spaces in paths	Unquoted variables → broke on spaces	All variables quoted → spaces handled safely
Path normalization	None	realpath -m ensures canonical, valid paths
Empty cache entries	Not handled	Guard added → falls back to default
Relative paths	Could slip through	Enforced absolute paths only
Symlink handling	Not checked	Detects broken symlinks → falls back
File type validation	Any file accepted	Only valid image extensions allowed
Default fallback	Limited checks	Robust fallback in all failure cases

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Note to Maintainers:

Thank you for reviewing this contribution. The changes are focused on improving reliability and robustness without altering existing functionality. I appreciate your time and feedback, and I’m happy to make any adjustments if needed.

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[rajghosh06-dev]

Related/Similar Issues:

• (already closed) Addresses concerns raised in [BUG] Allow spaces in Wallpaper file names #1047

• Relates to [BUG] wallpaper modes/blur not turning off #1426 (Wallpaper modes/blur not turning off)

• Relates to [FEATURE] Daily Wallpaper #1442 (Daily Wallpaper automation enhancement)

• Relates to Arch system package update broke waypaper and pywalfox #1394 (Waypaper/Pywalfox breaking wallpaper restore)

• Any other related to Wallpaper Automation Problem & Restore the last used Wallpaper before/after Restart or after a Full Shutdown.