bees: fix further instances of copy-after-unlock bug

Before:

        unique_lock<mutex> lock(some_mutex);
        // run lock.~unique_lock() because return
        // return reference to unprotected heap
        return foo[bar];

After:

        unique_lock<mutex> lock(some_mutex);
        // make copy of object on heap protected by mutex lock
        auto tmp_copy = foo[bar];
        // run lock.~unique_lock() because return
        // pass locally allocated object to copy constructor
        return tmp_copy;

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

src/bees-roots.cc

@@ -822,7 +822,8 @@ BeesCrawl::peek_front()
 	if (m_extents.empty()) {
 		return BeesFileRange();
 	}
-	return *m_extents.begin();
+	auto rv = *m_extents.begin();
+	return rv;
 }
 
 BeesFileRange
@@ -848,7 +849,8 @@ BeesCrawlState
 BeesCrawl::get_state()
 {
 	unique_lock<mutex> lock(m_state_mutex);
-	return m_state;
+	auto rv = m_state;
+	return rv;
 }
 
 void