Fixed AudFormat and WavFormat implementations of ISoundFormat.LengthInSeconds

- Fixed a rounding issue in `WavReader.WaveLength()`.
- Fixed `AudReader.SoundLength()` not resetting the stream position.
- Fixed crashes caused by disposed streams because `LengthInSeconds` would try and calculate the length on the fly. It is now precalculated and cached (making it consistent across all 5 current `ISoundFormat` implementations).
- Fixed a crash in `AudReader.LoadSound()`'s `out Func<Stream> result` because that func would try and access the disposed stream's `Length` property. That works for `SegmentStream`, but not for `FileStream`.
- Fixed frameCount/soundLength label positioning in the AssetBrowser window to avoid text clipping .

OpenRA.Mods.Cnc/FileFormats/AudReader.cs

@@ -34,6 +34,8 @@ namespace OpenRA.Mods.Cnc.FileFormats
 	{
 		public static float SoundLength(Stream s)
 		{
+			var originalPosition = s.Position;
+
 			var sampleRate = s.ReadUInt16();
 			/*var dataSize = */ s.ReadInt32();
 			var outputSize = s.ReadInt32();
@@ -46,6 +48,8 @@ namespace OpenRA.Mods.Cnc.FileFormats
 			if ((flags & SoundFlags._16Bit) != 0)
 				samples /= 2;
 
+			s.Seek(originalPosition, SeekOrigin.Begin);
+
 			return (float)samples / sampleRate;
 		}
 
@@ -70,10 +74,12 @@ namespace OpenRA.Mods.Cnc.FileFormats
 					throw new NotImplementedException();
 
 				var offsetPosition = s.Position;
+				var streamLength = s.Length;
+				var segmentLength = (int)(streamLength - offsetPosition);
 
 				result = () =>
 				{
-					var audioStream = SegmentStream.CreateWithoutOwningStream(s, offsetPosition, (int)(s.Length - offsetPosition));
+					var audioStream = SegmentStream.CreateWithoutOwningStream(s, offsetPosition, segmentLength);
 					return new AudStream(audioStream, outputSize, dataSize);
 				};
 			}