Ensure that netstandard is always checked before System.Runtime

ICSharpCode.Decompiler/Metadata/DotNetCorePathFinderExtensions.cs

@@ -98,15 +98,32 @@ namespace ICSharpCode.Decompiler.Metadata
 						case "netstandard":
 							version = r.Version.ToString(2);
 							return $".NETStandard,Version=v{version}";
-						case "System.Runtime":
+					}
-						case "System.Private.CoreLib":
+				}
+				catch (BadImageFormatException)
+				{
+					// ignore malformed references
+				}
+			}
+
+			// We check for System.Runtime separately because .NET Standard assemblies can reference it transitively,
+			// and we want to avoid detecting .NET Core for .NET Standard assemblies.
+			foreach (var h in metadata.AssemblyReferences)
+			{
+				try
+				{
+					var r = metadata.GetAssemblyReference(h);
+					if (r.PublicKeyOrToken.IsNil)
+						continue;
+					if (metadata.GetString(r.Name) is "System.Runtime" or "System.Private.CoreLib")
+					{
 						// System.Runtime.dll uses the following scheme:
 						// 4.1.0 => .NET Core 1.0 / 1.1
 						// 4.2.0 => .NET Core 2.0
 						// 4.2.1 => .NET Core 2.1 / 3.0
 						// 4.2.2 => .NET Core 3.1
 						// 5.0.0+ => .NET 5+
-							version = (r.Version.Major, r.Version.Minor, r.Version.Build) switch {
+						string version = (r.Version.Major, r.Version.Minor, r.Version.Build) switch {
 							(4, 1, 0) => "1.1",
 							(4, 2, 0) => "2.0",
 							(4, 2, 1) => "3.0",