fix error when sending thumbnail to master

Based on patch [#28108] by Wintch Analyzer

by Wintch Analyzer 

moving master working path initialization before connection creation

also added error checks and prints to debug an invalid internal state (related to another tracker entry)

- remove/comment unused variables
- remove unused imports
- fixed some bugs using incorrect variables

better stream handling when uploading files
Might solve the problem with OS X masters