Fix recovery tool empty file restore and other bugs

[Jojo-1000]

Closes #4884

• Fix missing block error message when restoring empty files, which were not restored
• Fix bug when restoring backup that only contains one file with recovery tool
• Fix path separator issues when recovering a Windows backup on Linux
• Fix one unnecessary level of directories in restore path
• Add unit tests for restore paths and add empty file to existing test case

Steps to reproduce (single file error)

• Create unencrypted local backup with only one source file (test.txt)
• Run recoverytool index . in destination folder
• Run recoverytool restore . --targetfolder=restore

Current behavior

• Output: Removing common prefix ...\source\test.txt\
• Error: System.ArgumentOutOfRangeException

New behavior

• Output: Removing common prefix ...\source\
• No error

Steps to reproduce (empty file error)

• Create unencrypted local backup (with at least two files) and one empty file
• Run recoverytool index . in destination folder
• Run recoverytool restore . --targetfolder=restore

Current behavior

• Error: System.Exception: Unable to locate block with hash: 47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=
• Empty files are not restored

New behavior

• No error
• Empty files are restored (without metadata like all files)

Steps to reproduce (unnecessary directory level)

• Create unencrypted local backup (with at least two files that are not empty) in folder source
• Run recoverytool index . in destination folder
• Run recoverytool restore . --targetfolder=restore

Current behavior

• Files are restore to restore\source
• restore contains only the single folder source that could be removed from the prefix

New behavior

• Files are restored to restore directly

Steps to reproduce (directory separators)

• Requires Linux/macOS (Windows accepts slashes as separators)
• Copy test backup from Windows install, or create unencrypted Linux/macOS backup and replace paths in dlist.zip with Windows paths including backslashes
• Run recoverytool index . in destination folder
• Run recoverytool restore . --targetfolder=restore

Current behavior

• Files are restored without a folder, instead they have the path including backslashes as a filename

New behavior

• Files are restored with the original folder structure