Consistent supports

Author: FlorianRappl

src/AngleSharp.Io/Network/AboutRequester.cs

@@ -69,7 +69,7 @@ public Task<IResponse> RequestAsync(IRequest request, CancellationToken cancel)
         /// <returns>True if the protocol is supported, otherwise false.</returns>
         public Boolean SupportsProtocol(String protocol)
         {
-            return !String.IsNullOrEmpty(protocol) && protocol.Equals("about");
+            return protocol.Equals("about", StringComparison.OrdinalIgnoreCase);
         }
 
         private static String GetAddress(String data)

src/AngleSharp.Io/Network/FileRequester.cs

@@ -45,7 +45,7 @@ public async Task<IResponse> RequestAsync(IRequest request, CancellationToken ca
         /// <returns>True if the protocol is supported, otherwise false.</returns>
         public Boolean SupportsProtocol(String protocol)
         {
-            return !String.IsNullOrEmpty(protocol) && protocol.Equals(ProtocolNames.File);
+            return protocol.Equals(ProtocolNames.File, StringComparison.OrdinalIgnoreCase);
         }
     }
 }

src/AngleSharp.Io/Network/FtpRequester.cs

@@ -48,7 +48,7 @@ public async Task<IResponse> RequestAsync(IRequest request, CancellationToken ca
         /// <returns>True if the protocol is supported, otherwise false.</returns>
         public Boolean SupportsProtocol(String protocol)
         {
-            return !String.IsNullOrEmpty(protocol) && protocol.Equals(ProtocolNames.Ftp);
+            return protocol.Equals(ProtocolNames.Ftp, StringComparison.OrdinalIgnoreCase);
         }
     }
 }