Reset encoding mode to default for codecs with dynamic modes list,

when settings become incompatible with the chosen mode.
E.g. for flac if -11 was selected and nonsubset modes are disabled,
-7 is chosen instead.

CUETools.Codecs.FLAKE/FlakeWriter.cs

@@ -37,12 +37,13 @@ namespace CUETools.Codecs.FLAKE
     public class FlakeWriterSettings : AudioEncoderSettings
     {
         public FlakeWriterSettings()
-            : base("", "7")
+            : base()
         {
         }
 
-        public override string GetSupportedModes()
+        public override string GetSupportedModes(out string defaultMode)
         {
+            defaultMode = "7";
             return this.AllowNonSubset ? "0 1 2 3 4 5 6 7 8 9 10 11" : "0 1 2 3 4 5 6 7 8";
         }