bp_detect_theme_compat_with_current_theme(), bp_core_load_template() don't work for themes with /bp-legacy copied files inside them

[lenasterg]

Hi.
I noticed that the bp_detect_theme_compat_with_current_theme() and bp_core_load_template() aren't compatible with themes which follow the guidelines from ​https://codex.buddypress.org/themes/theme-compatibility-1-7/a-quick-look-at-1-7-theme-compatibility/#overloading-template-compatibility-theme-files and have a copy from bp-legacy/ files into either theme's /buddypress subfolder or theme/community subfolder.

It seems to me as a bug. Attached is the suggested patch.