Fix: Undefined Array Key in `wp_image_add_srcset_and_sizes` function

[Debarghya-Banerjee]

Trac Ticket: Core-60480

Description

• This pull request addresses a warning encountered during the media import process when using the "Download and import file attachments" option in the Tools > Import section of WordPress. A warning is triggered due to an attempt to access an undefined array key in the wp_image_add_srcset_and_sizes function.

Proposed Changes

• Added an isset() check before accessing the 'file' key of the $image_meta array to prevent the warning from occurring.

• This adjustment ensures that the code handles cases where media metadata retrieval fails more gracefully, avoiding the warning message.

• Additionally, this change is aimed at bringing consistency across all functions that interact with attachment metadata, ensuring that similar checks are uniformly applied throughout the codebase.