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-context.cc

@@ -969,7 +969,8 @@ BeesContext::tmpfile()
 	if (!m_tmpfiles[this_thread::get_id()]) {
 		m_tmpfiles[this_thread::get_id()] = make_shared<BeesTempFile>(shared_from_this());
 	}
-	return m_tmpfiles[this_thread::get_id()];
+	auto rv = m_tmpfiles[this_thread::get_id()];
+	return rv;
 }
 
 shared_ptr<BeesFdCache>
@@ -980,7 +981,8 @@ BeesContext::fd_cache()
 	if (!m_fd_cache) {
 		m_fd_cache = make_shared<BeesFdCache>();
 	}
-	return m_fd_cache;
+	auto rv = m_fd_cache;
+	return rv;
 }
 
 shared_ptr<BeesRoots>
@@ -991,7 +993,8 @@ BeesContext::roots()
 	if (!m_roots) {
 		m_roots = make_shared<BeesRoots>(shared_from_this());
 	}
-	return m_roots;
+	auto rv = m_roots;
+	return rv;
 }
 
 shared_ptr<BeesHashTable>
@@ -1002,7 +1005,8 @@ BeesContext::hash_table()
 	if (!m_hash_table) {
 		m_hash_table = make_shared<BeesHashTable>(shared_from_this(), "beeshash.dat");
 	}
-	return m_hash_table;
+	auto rv = m_hash_table;
+	return rv;
 }
 
 void

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

src/bees-types.cc

@@ -286,7 +286,8 @@ Fd
 BeesFileRange::fd() const
 {
 	unique_lock<mutex> lock(s_mutex);
-	return m_fd;
+	auto rv = m_fd;
+	return rv;
 }
 
 Fd
@@ -310,7 +311,8 @@ BeesFileRange::fd(const shared_ptr<BeesContext> &ctx) const
 		}
 	}
 	// We either had a fid and opened it, or we didn't and we're just stuck with our fd
-	return m_fd;
+	auto rv = m_fd;
+	return rv;
 }
 
 BeesFileRange