Handle the empty registry cache file

[mxchist]

I ran into the same issue as described in #502. In my case, the JS ERROR: SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 was caused by an empty registry file (registry.txt).

Unfortunately, the issue appears to have started quite some time ago (likely in the second half of 2024). I postponed investigating why the extension stopped working until this week, and by now I can no longer determine what originally caused the registry file to be emptied.

[mxchist]

I attempted to make the registry file empty by:

• pressing the 🗑️ Clear history button;
• manually deleting all history entries one by one;
• enabling the "Clear history on system reboot" option.
  None of these actions resulted in an empty cache file; therefore, the file never became invalid input for JSON.parse.