Avoid invalid expression and type mismatch

Invalid expression error is produced when trying to open certain tags: This avoids the error:

Error detected while processing function <SNR>57_AcceptSelection:
line   30:
E685: Internal error: get_tv_string_buf()
E15: Invalid expression: type == 'dict' ? [{ 'action': md, 'line': line, 'icr': icr }] : [md, line]
line   31:
E121: Undefined variable: actargs
E116: Invalid arguments for function call