Dont clone figure.layout

[almarklein]

Fixes #879 (hopefully)

This small changes fixes the issue (for e.g. the example below). That said, I cannot oversee whether this potentially breaks other code. In theory, the tests will tell ;)

Example to test this:

import dash
import dash_html_components as html
import dash_core_components as dcc
from dash.dependencies import Input, Output, State


app = dash.Dash(__name__, update_title=None)

fig = {"data": [], "layout": {"dragmode": "drawrect"}}
graph = dcc.Graph(id="graph", figure=fig)

app.layout = html.Div(
    [
        graph,
        html.Br(),
        html.Button(id='button', children="Clone figure"),
        html.Div(id='output', children=""),
    ]
)

app.clientside_callback(
    """function clone_figure(_, figure) {
        let new_figure = {...figure};
        let shapes = new_figure.layout.shapes || [];
        return [new_figure, shapes.length];
    }
    """,
    [Output("graph", "figure"), Output("output", "children")],
    [Input("button", "n_clicks")],
    [State("graph", "figure")],
)



if __name__ == "__main__":
    app.run_server(debug=True)