Fix IndexError in _get_var_node

[ericwb]

Traceback (most recent call last):
  File "/Users/ericwb/workspace/precli/precli/cli/main.py", line 192, in parse_file
    return parser.parse(fname, data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ericwb/workspace/precli/precli/parsers/__init__.py", line 81, in parse
    self.visit([tree.root_node])
  File "/Users/ericwb/workspace/precli/precli/parsers/__init__.py", line 102, in visit
    visitor_fn(node.children)
  File "/Users/ericwb/workspace/precli/precli/parsers/python.py", line 34, in visit_module
    self.visit(nodes)
  File "/Users/ericwb/workspace/precli/precli/parsers/__init__.py", line 102, in visit
    visitor_fn(node.children)
  File "/Users/ericwb/workspace/precli/precli/parsers/__init__.py", line 102, in visit
    visitor_fn(node.children)
  File "/Users/ericwb/workspace/precli/precli/parsers/python.py", line 127, in visit_assignment
    self.visit(nodes)
  File "/Users/ericwb/workspace/precli/precli/parsers/__init__.py", line 102, in visit
    visitor_fn(node.children)
  File "/Users/ericwb/workspace/precli/precli/parsers/__init__.py", line 102, in visit
    visitor_fn(node.children)
  File "/Users/ericwb/workspace/precli/precli/parsers/__init__.py", line 102, in visit
    visitor_fn(node.children)
  File "/Users/ericwb/workspace/precli/precli/parsers/python.py", line 133, in visit_call
    call = Call(
           ^^^^^
  File "/Users/ericwb/workspace/precli/precli/core/call.py", line 27, in __init__
    self._var_node = Call._get_var_node(self._func_node)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ericwb/workspace/precli/precli/core/call.py", line 35, in _get_var_node
    and node.named_children[1].type == "identifier"
        ~~~~~~~~~~~~~~~~~~~^^^
IndexError: list index out of range