Fix blocking callback bug

[lcornelatti]

Changes summary

• Add try, except block around calling of function in blocking callback transform
• If callback fails due to an exception, return no_update in all outputs, but still return current timestamp to end_server_id component.

Reason for changes

• Current code has a bug. If a blocking callback fails due to an exception being thrown, the callback will never be triggered again
• This is due to the end_server_id never being updated upon failure of the callback. In further calls of the callback, the clientside callback that ensures the blocking behaviour still thinks the previous callback is being ran. This is only released after blocking_timeout

Testing

• The behaviour can be reproduced with the example given.
• By applying these changes the callback is unblocked

from dash_extensions.enrich import Dash, dcc, html, Input, Output, callback

app = Dash(__name__)

app.layout = html.Div([
    html.Div([
        "Input: ",
        dcc.Input(id='my-input', value='initial value', type='text')
    ]),
    html.P(id='my-output')
])

i = 0

@callback(
    Output('my-output', 'children'),
    Input('my-input', 'value'),
    prevent_initial_call=True,
    blocking=True,
)
def check_input(input_value):
    global i
    i += 1
    if input_value == "bad":
        raise Exception(f'input is bad! {i}')
    return i

if __name__ == '__main__':
    app.run(debug=False)

[lcornelatti]

Hey @emilhe , would appreciate a review here

[emilhe]

@lcornelatti Thanks for the PR! This is most definitly a bug. I have made a single suggestion for an improvement. Once that is cleared out, I believe the PR can be merged.

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (4392117) 80.45% compared to head (24a8ae3) 80.35%. Report is 2 commits behind head on master.

Files	Patch %	Lines
dash_extensions/enrich.py	77.77%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #309 +/- ## ========================================== - Coverage 80.45% 80.35% -0.10% ========================================== Files 10 10 Lines 1018 1023 +5 ========================================== + Hits 819 822 +3 - Misses 199 201 +2 ```

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