Transformer.__default__ not called in tree-less LALR mode

[RoadrunnerWMC]

Describe the bug

The __default__ method on Transformers is never called when using "Tree-less LALR" mode.

To Reproduce

Here's an example based on "ab.lark" from the unit tests. __default__() should be called for every rule here, but when using tree-less LALR mode (change BUILD_TREE to False), it's not called at all.

from lark import Lark, Transformer

BUILD_TREE = True  # Change to False to try tree-less LALR mode

grammar = r"""
    start: expr

    expr: A B
        | A expr B

    A: "a"
    B: "b"

    %import common.WS
    %ignore WS
"""

class AbTransformer(Transformer):
    def __default__(self, data, children, meta):
        print(f'__default__({data!r}, {children!r}, {meta!r})')
        return data

def parse(x):
    if BUILD_TREE:
        parser = Lark(grammar, parser='lalr')
        return AbTransformer().transform(parser.parse(x))
    else:
        parser = Lark(grammar, parser='lalr', transformer=AbTransformer())
        return parser.parse(x)

print(parse('a a a b b b'))  # should print "start"

[erezsh]

A fix is ready. See #1036