fix endless loop in FIND_NEXT2

[HynekPetrak]

This fixes an endless loop between client and server in certain situations, when there is more files then fits into a single response.

According to https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-cifs/80dc980e-fe03-455c-ada6-7c5dd6c551ba the ResumeKey parameter within FIND_NEXT2 request is mandatory and shall be equal to a value of FileIndex of the last file from the previous response. of FIND_FIRST2 or FIND_NEXT2, according: https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-cifs/891140f4-45fc-4a7c-801d-f182a29ed4d1

Confirmed through a tcpdump of smbclient interracting with the same host, where impacket enters the endless loop.