let FileInput widget set filename

[ltalirz]

fixes #955

The value of the filename property of the FileInput always remained
None (also after uploading a file).

I could add a test here, if you let me know what the filename I should be testing for here.

[codecov]

Codecov Report

Merging #956 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #956      +/-   ##
=========================================
+ Coverage   85.05%   85.1%   +0.05%     
=========================================
  Files          96      96              
  Lines       10637   10685      +48     
=========================================
+ Hits         9047    9094      +47     
- Misses       1590    1591       +1

Impacted Files	Coverage Δ
panel/tests/widgets/test_input.py	100% <100%> (ø)	⬆️
panel/widgets/input.py	97.92% <100%> (ø)	⬆️
panel/tests/pane/test_markup.py	99.2% <0%> (-0.8%)	⬇️
panel/tests/test_io.py	100% <0%> (ø)	⬆️
panel/models/markup.py	100% <0%> (ø)	⬆️
panel/pane/markup.py	95.95% <0%> (+0.46%)	⬆️
panel/pane/base.py	87.2% <0%> (+0.54%)	⬆️

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[philippjfr]

This is great thank you!

I could add a test here, if you let me know what the filename I should be testing for here.

Just do something like this:

file_input._comm_change({'mime_type': 'text/plain', 'value': 'U29tZSB0ZXh0Cg==', 'filename': 'testfile'})

assert file_input.filename == 'testfile'

[ltalirz]

Done!

[philippjfr]

Looks like a syntax error snuck in there.

[philippjfr]

Thanks again!