Don't try setting the audio input source if the v4l2 device doesn't have any.

modules/access/v4l2.c

@@ -1897,7 +1897,12 @@ static int OpenVideoDev( vlc_object_t *p_obj, demux_sys_t *p_sys, vlc_bool_t b_d
         goto open_failed;
     }
 
-    if( p_sys->i_selected_audio_input >= p_sys->i_audio )
+    /* Set audio input */
+
+    if( p_sys->i_audio > 0 )
+    {
+        if( p_sys->i_selected_audio_input < 0
+         || p_sys->i_selected_audio_input >= p_sys->i_audio )
         {
             msg_Warn( p_obj, "invalid audio input. Using the default one" );
             p_sys->i_selected_audio_input = 0;
@@ -1908,6 +1913,8 @@ static int OpenVideoDev( vlc_object_t *p_obj, demux_sys_t *p_sys, vlc_bool_t b_d
             msg_Err( p_obj, "cannot set audio input (%m)" );
             goto open_failed;
         }
+        msg_Dbg( p_obj, "Audio input set to %d", p_sys->i_selected_audio_input );
+    }
 
 
     /* TODO: Move the resolution stuff up here */