Never generate empty backup name

* Backup would then go to /sdcard/TWRP/*serial_num*/
  (without any subfolder) and restore would not be able to find it.

Signed-off-by: Vojtech Bocek <vbocek@gmail.com>
Remove unneeded images
Merge "Remove unneeded images" into twrp2.7
check for space after = too
Improvements to Update_Log_File

Change-Id: I5596759b0cb39e4448b6be382f9224feed70a5ea
Fix checking for file_contexts in updater
Merge "Fix checking for file_contexts in updater" into twrp2.7
Merge "Improvements to Update_Log_File" into twrp2.7
Merge "check for space after = too" into twrp2.7