playlist: use playlist_Play() directly, fix minor races

This function already checks if the playlist is running internally,
in which case it has no effects.

modules/control/dbus/dbus_player.c

@@ -208,14 +208,7 @@ DBUS_METHOD( Stop )
 DBUS_METHOD( Play )
 {
     REPLY_INIT;
-    input_thread_t *p_input =  pl_CurrentInput( p_this );
-
-    if( !p_input || var_GetInteger( p_input, "state" ) != PLAYING_S )
-        playlist_Play( PL );
-
-    if( p_input )
-        vlc_object_release( p_input );
-
+    playlist_Play( PL );
     REPLY_SEND;
 }
 

modules/gui/qt4/input_manager.cpp

@@ -1128,16 +1128,7 @@ void MainInputManager::togglePlayPause()
 
 void MainInputManager::play()
 {
-    /* No input, play */
-    if( !p_input )
-        playlist_Play( THEPL );
-    else
-    {
-        if( PLAYING_S != var_GetInteger( p_input, "state" ) )
-        {
-            playlist_TogglePause( THEPL );
-        }
-    }
+    playlist_Play( THEPL );
 }
 
 void MainInputManager::pause()