list-view, grid-view: don't sort directories before files in search results

As described in #2968 (closed), directories are currently sorted before files in search results if this option is enabled in preferences, leading to less relevant results being shown first if they are directories.

This commit adds a call to real_sort_directories_first_changed() in real_begin_loading(), causing search results to ignore the sort directories first preference as intended.

Closes #2968 (closed)