Load assembly from full path before parsing it as an assembly name

clr.AddReference with a rooted path to a non-managed file (e.g. a native
library) should surface a BadImageFormatException. On Windows that happened
because new AssemblyName(@"C:\...\kernel32.dll") fails to parse, so the code
fell through to LoadAssemblyFullPath -> Assembly.LoadFrom -> BadImageFormat.

On Linux the path "/.../libpython3.10.so.1.0" parses fine as an AssemblyName,
so Assembly.Load(name) ran first and threw FileNotFoundException ("The system
cannot find the file specified") before LoadAssemblyFullPath was reached. This
broke the BadAssembly embedding test on Ubuntu.

Try LoadAssemblyFullPath (which loads an existing file from disk) before the
parse-as-assembly-name path, so a real file on disk yields BadImageFormatException
consistently across platforms. Non-rooted names are unaffected and still fall
through to Assembly.Load.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jhonabreul

src/runtime/Types/ModuleObject.cs

@@ -505,14 +505,19 @@ public static Assembly AddReference(string name)
             {
                 assembly = AssemblyManager.LoadAssemblyPath(name);
             }
-            if (assembly == null && AssemblyManager.TryParseAssemblyName(name) is { } parsedName)
-            {
-                assembly = AssemblyManager.LoadAssembly(parsedName);
-            }
+            // Try loading an existing file on disk before parsing the name as an
+            // assembly name. A rooted path (e.g. a native library) can parse as a
+            // valid AssemblyName on some platforms, which would make Assembly.Load
+            // throw FileNotFoundException instead of letting Assembly.LoadFrom open
+            // the file and surface the real BadImageFormatException.
             if (assembly == null)
             {
                 assembly = AssemblyManager.LoadAssemblyFullPath(name);
             }
+            if (assembly == null && AssemblyManager.TryParseAssemblyName(name) is { } parsedName)
+            {
+                assembly = AssemblyManager.LoadAssembly(parsedName);
+            }
             if (assembly == null)
             {
                 throw new FileNotFoundException($"Unable to find assembly '{name}'.");