[BUG]: plotly.js DevTools crashes if malformed JSON file exists in mocks folder

[camdecoster]

Description

Running npm start starts up plotly.js DevTools. If a malformed JSON exists in the mocks folder (test/image/mocks), this process will crash and the dev server won't start. The script should be updated to handle this situation.

Steps to reproduce

• Add an empty JSON file to the mocks folder:

  touch test/image/mocks/empty_file.json

• Run npm start
• Note that the process crashes

  $ npm start
  
  > plotly.js@3.3.0 start
  > node devtools/test_dashboard/server.mjs
  
  undefined:1
  
  
  SyntaxError: Unexpected end of JSON input
      at JSON.parse (<anonymous>)
      at file:///home/cam/Development/plotly/plotly.js/devtools/dashboard_utilities.mjs:43:31
      at Array.map (<anonymous>)
      at createMocksList (file:///home/cam/Development/plotly/plotly.js/devtools/dashboard_utilities.mjs:42:33)
      at async file:///home/cam/Development/plotly/plotly.js/devtools/test_dashboard/server.mjs:19:1
  
  Node.js v18.20.8