Kernel: Suppress remaining unobserved KResult return codes

These are all cases where there is no clear and easy fix,
I've left FIXME bread crumbs so that these can hopefully
be fixed over time.

Kernel/FileSystem/Ext2FileSystem.cpp

@@ -1477,11 +1477,13 @@ void Ext2FSInode::populate_lookup_cache() const
         return;
     HashMap<String, unsigned> children;
 
-    traverse_as_directory([&children](auto& entry) {
+    KResult result = traverse_as_directory([&children](auto& entry) {
         children.set(String(entry.name, entry.name_length), entry.inode.index());
         return true;
     });
 
+    ASSERT(result.is_success());
+
     if (!m_lookup_cache.is_empty())
         return;
     m_lookup_cache = move(children);