Return to Answer

You didn't create any partition. Instead the MBR got bogus by using GParted. Probably the CoreStorage LVG and all subsequent containers got corrupted also. Additionally the recovery partition wasn't moved properly. But this a different problem.

GParted didn't really create unallocated disk space. Instead the MBR got bogus. The CoreStorage LVG and all subsequent containers got corrupted also, because the whole stack wasn't resized as required. Usually - in macOS - the whole stack is resized with the command diskutil cs resizeStack .... As far as I can say from remote, the ending boundary of the second partition was simply moved to lower block numbers which usually works with normal HFS+ volumes in GParted but not in this case with a CoreStorage stack. Fortunately some invisible data structures of the CS stack weren't overwritten.

Additionally the recovery partition wasn't moved properly. But this a different problem.

If the Logical Volume doesn't appear or if the disk verification fails, report back and leave a comment.

If the Logical Volume Family and the Logical Volume don't appear try the following:

If the Logical Volume Family and the Logical Volume don't appear try the following:

If you get errors backup the data or the whole partition to an external volume then repair the volume with diskutil repairVolume disk17. One possibility to backup the data is dd. Attach a HFS+ formatted drive with at least 250 GB free space. Get the path to the external volume with ls /Volumes. Then unmount disk17 and disk0 with diskutil umountDisk disk17 and diskutil umountDisk disk0. Then clone the partition to a file: dd if=/dev/disk0s2 of=/Volumes/ExternalDriveName/disk0s2.rawdevice bs=4m. If the volume name contains spaces, escape the spaces with backslashes: ...of=/Volumes/ExternalDriveName\ With\ Spaces/disk0s2.rawdevice....

If you get errors backup the data or the whole partition to an external volume then repair the volume with diskutil repairVolume disk17. 

One possibility to backup the data is dd. Attach a HFS+ formatted drive with at least 250 GB free space. Get the path to the external volume with ls /Volumes. Then unmount disk17 and disk0 with diskutil umountDisk disk17 and diskutil umountDisk disk0. 

Then clone the partition to a file:

    dd if=/dev/disk0s2 of=/Volumes/ExternalDriveName/disk0s2.rawdevice bs=4m

If the volume name contains spaces, escape the spaces with backslashes: ...of=/Volumes/ExternalDriveName\ With\ Spaces/disk0s2.rawdevice....

You can also use asr to restore the partition to another disk (as a temporary "backup"). Check man asr.