Use string.Contains(char) instead of (string)

CA1847: Use string.Contains(char) instead of string.Contains(string) with single characters
https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1847

Author: decriptor

src/TaglibSharp/Picture.cs

@@ -365,7 +365,7 @@ public Picture (File.IFileAbstraction abstraction)
 			Filename = abstraction.Name;
 			Description = abstraction.Name;
 
-			if (!string.IsNullOrEmpty (Filename) && Filename.Contains (".")) {
+			if (!string.IsNullOrEmpty (Filename) && Filename.Contains ('.')) {
 				MimeType = GetMimeFromExtension (Filename);
 				Type = MimeType.StartsWith ("image/") ? PictureType.FrontCover : PictureType.NotAPicture;
 			} else {

src/TaglibSharp/PictureLazy.cs

@@ -148,7 +148,7 @@ public PictureLazy (File.IFileAbstraction abstraction, long offset = 0, long siz
 			filename = abstraction.Name;
 			Description = abstraction.Name;
 
-			if (!string.IsNullOrEmpty (filename) && filename.Contains (".")) {
+			if (!string.IsNullOrEmpty (filename) && filename.Contains ('.')) {
 				mime_type = Picture.GetMimeFromExtension (filename);
 				type = mime_type.StartsWith ("image/") ? PictureType.FrontCover : PictureType.NotAPicture;
 			}