Avoid corrupting strings when replaceLastOccurrence does not find the search fragment

[javihgil]

Problem

assumes the search fragment exists in the source string.

When it does not, returns and the current implementation can return a corrupted string.

Impact

• index updates can become fragile in unexpected HTML structures
• id or full-name rewriting may produce broken markup instead of leaving the string unchanged

Expected behavior

If the search fragment is not found, the function should return the original string unchanged.