Bug report: PBKDF2-same output for different inputs

When I use the salt same outputs occures for different inputs.
Link to reproduce:
https://gchq.github.io/CyberChef/#recipe=Fork('%5C%5Cn','%5C%5Cn',false)Derive_PBKDF2_key(%7B'option':'UTF8','string':''%7D,128,1,'SHA1',%7B'option':'UTF8','string':'anysalt'%7D)&input=aW5wdXQxCmlucHV0MgppbnB1dDM

Without salt they are different.
I'm using it in Firefox browser on Win10.

Start with the linked CyberChef recipe and its Derive_PBKDF2_key operation, reproducing the salted case in Firefox with the three inputs shown. Compare the derived outputs for different inputs and verify that the fix preserves the distinct unsalted outputs; done means different inputs no longer produce the same salted result.

Written by the indexing model from the issue text.