PHP 8.2 Legacy Error in WebClient.php not solved by #42830

[ssabatini]

Steps to reproduce the issue

View PHP Error log for Joomla site with PHP 8.2.X.
Look for warnings "stripos(): Passing null to parameter #1 ($haystack) of type string is deprecated ..."

Expected result

No warnings regarding "stripos(): Passing null to parameter #1 ($haystack) of type string is deprecated ..." anymore.

Actual result

#42830 has fixed this warning only in the function detectBrowser(), but the same warning (with the same reason) is produced by the functions detectEngine() and detectPlatform().

Additionally, the function detectRobot() does as well not test if the user agent is null.

[alikon]

please check joomla-framework/application#124

[ssabatini]

@alikon The fix looks good. The first fix with issue #42830 should be unnecessary now; the if ($userAgent !== null) in the method detectBrowser can be removed.