aout: the stop implementation is now mandatory

include/vlc_aout.h

@@ -159,7 +159,7 @@ struct audio_output
       */
 
     void (*stop)(audio_output_t *);
-    /**< Stops the existing stream (optional, may be NULL).
+    /**< Stops the existing stream (mandatory, cannot be NULL).
       *
       * This callback terminates the current audio stream,
       * and returns the audio output to stopped state.

src/audio_output/output.c

@@ -609,8 +609,7 @@ int aout_OutputNew (audio_output_t *aout, audio_sample_format_t *restrict fmt,
 void aout_OutputDelete (audio_output_t *aout)
 {
     aout_OutputLock(aout);
-    if (aout->stop != NULL)
-        aout->stop (aout);
+    aout->stop (aout);
     aout_OutputUnlock(aout);
 }