Fixed [error] Type (::Array[::String] | nil) does not have method join

```
lib/ruby_header_parser/parser.rb:304:55: [error] Type `(::Array[::String] | nil)` does not have method `join`
│ Diagnostic ID: Ruby::NoMethod
│
└       original_type = Util.sanitize_type(parts[0...-1].join(" "))
                                                         ~~~~
```

Author: sue445

lib/ruby_header_parser/parser.rb

@@ -301,7 +301,8 @@ def generate_argument_definition(function_name:, arg:, arg_pos:)
     #   - length [Integer]
     def analyze_argument_type(function_name:, arg_pos:, parts:)
       pointer, length = prepare_argument_parts(arg_pos:, parts:)
-      original_type = Util.sanitize_type(parts[0...-1].join(" "))
+      type = parts[0...-1] || []
+      original_type = Util.sanitize_type(type.join(" "))
 
       case original_type
       when /\*+$/