Limit offset to max len in com_search

[HLeithner]

Pull Request for Issue #30501 .

Summary of Changes

Limit the offset length to textlength

Testing Instructions

Create a test side with short and long articles and search for a word using php 8

Actual result BEFORE applying this Pull Request

search error 0 mb_strpos(): Argument #3 ($offset) must be contained in argument #1 ($haystack)

Expected result AFTER applying this Pull Request

Get a search result

[bayareajenn]

I have tested this item ✅ successfully on 5affcda

After applying patch, com_search works with PHP8. Thanks Harald.

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[alikon]

I have tested this item ✅ successfully on 5affcda

php8 rc4

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[alikon]

RTC

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[richard67]

Thanks!