ifcopenshell.open - readable error if file doesn't exist

Previously it would show obscure error like:

RuntimeError: Type held at index 0 is class Blank and not class std::vector<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::allocator<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > >

src/ifcopenshell-python/ifcopenshell/__init__.py

@@ -156,6 +156,8 @@ def open(
         print(products[0] == model[122] == model["2XQ$n5SLP5MBLyL442paFx"]) # True
     """
     path = Path(path)
+    if not path.exists():
+        raise FileNotFoundError(f"File does not exist: '{path}'.")
     if format is None:
         format = guess_format(path)
     if format == ".ifcXML":