Fixed the null reference exception prompted when downloading pure music.

tests/ZonyLrcTools.Tests/Infrastructure/Lyric/KuGouLyricDownloaderTests.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Linq;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using Shouldly;
 using Xunit;

tests/ZonyLrcTools.Tests/Infrastructure/Lyric/NetEaseLyricDownloaderTests.cs

@@ -69,5 +69,13 @@ namespace ZonyLrcTools.Tests.Infrastructure.Lyric
 
             lyric.ShouldNotBeNull();
         }
+
+        [Fact]
+        public async Task UnknownIssue_Test()
+        {
+            var lyric = await _lyricDownloader.DownloadAsync("主題歌Arrietty's Song", "Cécile Corbel");
+
+            lyric.ShouldNotBeNull();
+        }
     }
 }