fix(renamer): fix generic name parsing null case (upstream mkaring#516)

When preserveGenericParams is true but name is null or empty,
ParseGenericName would crash. Add a null/empty guard to prevent this.

Cherry-pick of mkaring#516.

Author: RandomCrocodile

Confuser.Renamer/NameService.cs

@@ -214,7 +214,7 @@ public string ObfuscateName(IDnlibDef dnlibDef, RenameMode mode) {
 
 		public string ObfuscateName(string format, string name, RenameMode mode, bool preserveGenericParams = false) {
 			int genericParamsCount = 0;
-			if (preserveGenericParams) {
+			if (preserveGenericParams && !string.IsNullOrEmpty(name)) {
 				name = ParseGenericName(name, out genericParamsCount);
 			}