DetachedSong, db/LightSong, db/simple/Song: use std::chrono::system_clock::time_point

src/db/plugins/ProxyDatabasePlugin.cxx

@@ -197,7 +197,11 @@ ProxySong::ProxySong(const mpd_song *song)
 	uri = mpd_song_get_uri(song);
 	real_uri = nullptr;
 	tag = &tag2;
-	mtime = mpd_song_get_last_modified(song);
+
+	const auto _mtime = mpd_song_get_last_modified(song);
+	mtime = _mtime > 0
+		? std::chrono::system_clock::from_time_t(_mtime)
+		: std::chrono::system_clock::time_point::min();
 
 #if LIBMPDCLIENT_CHECK_VERSION(2,3,0)
 	start_time = SongTime::FromS(mpd_song_get_start(song));

src/db/plugins/simple/Song.cxx

@@ -29,7 +29,7 @@
 #include <string.h>
 
 inline Song::Song(const char *_uri, size_t uri_length, Directory &_parent)
-	:parent(&_parent), mtime(0),
+	:parent(&_parent), mtime(std::chrono::system_clock::time_point::min()),
 	 start_time(SongTime::zero()), end_time(SongTime::zero())
 {
 	memcpy(uri, _uri, uri_length + 1);

src/db/plugins/simple/Song.hxx

@@ -70,7 +70,11 @@ struct Song {
 	 */
 	Directory *const parent;
 
-	time_t mtime;
+	/**
+	 * The time stamp of the last file modification.  A negative
+	 * value means that this is unknown/unavailable.
+	 */
+	std::chrono::system_clock::time_point mtime;
 
 	/**
 	 * Start of this sub-song within the file.

src/db/plugins/upnp/UpnpDatabasePlugin.cxx

@@ -63,7 +63,7 @@ public:
 		uri = uri2.c_str();
 		real_uri = real_uri2.c_str();
 		tag = &tag2;
-		mtime = 0;
+		mtime = std::chrono::system_clock::time_point::min();
 		start_time = end_time = SongTime::zero();
 	}
 };
@@ -314,7 +314,7 @@ visitSong(const UPnPDirObject &meta, const char *path,
 	song.uri = path;
 	song.real_uri = meta.url.c_str();
 	song.tag = &meta.tag;
-	song.mtime = 0;
+	song.mtime = std::chrono::system_clock::time_point::min();
 	song.start_time = song.end_time = SongTime::zero();
 
 	if (selection.Match(song))