handle bad paths in sys.path

fixes pythonnet#2376

src/runtime/AssemblyManager.cs

@@ -200,6 +200,12 @@ static IEnumerable<string> FindAssemblyCandidates(string name)
                 }
                 else
                 {
+                    int invalidCharIndex = head.IndexOfAny(Path.GetInvalidPathChars());
+                    if (invalidCharIndex >= 0)
+                    {
+                        Exceptions.warn($"Path entry '{head}' has invalid char at position {invalidCharIndex}", Exceptions.ValueError);
+                        continue;
+                    }
                     path = Path.Combine(head, name);
                 }
 

tests/test_module.py

@@ -344,6 +344,20 @@ def test_clr_add_reference():
     with pytest.raises(FileNotFoundException):
         AddReference("somethingtotallysilly")
 
+
+def test_clr_add_reference_bad_path():
+    import sys
+    from clr import AddReference
+    from System.IO import FileNotFoundException
+    bad_path = "hello\0world"
+    sys.path.append(bad_path)
+    try:
+        with pytest.raises(FileNotFoundException):
+            AddReference("test_clr_add_reference_bad_path")
+    finally:
+        sys.path.remove(bad_path)
+
+
 def test_clr_get_clr_type():
     """Test clr.GetClrType()."""
     from clr import GetClrType