[XenForoBridge] Fix error if message is < 70 chars (#2707)
[XenForoBridge] Fix error if message is < 70 chars (#2707)

At the time of writing, this occurs on the following thread:
https://forum.xda-developers.com/t/optimized-lineageos19-1-v4-0-23apr.4426575/

Fixes the following error:
ValueError: strpos(): Argument #3 ($offset) must be contained in argument #1 ($haystack) in ./rss-bridge/bridges/XenForoBridge.php:272
Stack trace:
0 ./rss-bridge/bridges/XenForoBridge.php(272): strpos()
1 ./rss-bridge/bridges/XenForoBridge.php(146): XenForoBridge->extractThreadPostsV2()
2 ./rss-bridge/actions/DisplayAction.php(134): XenForoBridge->collectData()
3 ./rss-bridge/index.php(24): DisplayAction->execute()
4 {main}
RSS-Bridge/rss-bridge,Riduidel/rss-bridge,ORelio/rss-bridge,RSS-Bridge/rss-bridge,ORelio/rss-bridge,ORelio/rss-bridge,Riduidel/rss-bridge,RSS-Bridge/rss-bridge,Riduidel/rss-bridge