equalizer: load the equalizer-preset only if equalizer-bands is not set

When using the libVLC equalizer API, this prevents the band settings to be overridden on start by the default "flat" preset.

(cherry picked from commit 083b686c61404dd071327dea6a1766ab6f6c69eb)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/audio_filter/equalizer.c

@@ -341,11 +341,13 @@ static int EqzInit( filter_t *p_filter, int i_rate )
 
     /* Get initial values */
     var_Get( p_aout, "equalizer-preset", &val1 );
-    PresetCallback( VLC_OBJECT( p_aout ), NULL, val1, val1, p_sys );
-    free( val1.psz_string );
-
     var_Get( p_aout, "equalizer-bands", &val2 );
     var_Get( p_aout, "equalizer-preamp", &val3 );
+
+    /* Load the preset only if equalizer-bands is not set. */
+    if (val2.psz_string != NULL && *val2.psz_string != "\0")
+        PresetCallback( VLC_OBJECT( p_aout ), NULL, val1, val1, p_sys );
+    free( val1.psz_string );
     BandsCallback(  VLC_OBJECT( p_aout ), NULL, val2, val2, p_sys );
     PreampCallback( VLC_OBJECT( p_aout ), NULL, val3, val3, p_sys );