[volume.balance] panic: runtime error: index out of range [-1]

[kmlebedev]

> volume.balance
Running in simulation mode. Use "-force" option to apply the changes.
> volume.balance -dataCenter lol
Running in simulation mode. Use "-force" option to apply the changes.
panic: runtime error: index out of range [-1]

goroutine 1 [running]:
github.com/chrislusf/seaweedfs/weed/shell.balanceSelectedVolume(0xc000700000?, {0x0, 0x0}, 0x0?, {0x0, 0x0, 0x800?}, 0xc0005bd990, 0x26f7708, 0x0)
	/Users/tochka/GolandProjects/seaweedfs/weed/shell/command_volume_balance.go:262 +0x76c
github.com/chrislusf/seaweedfs/weed/shell.balanceVolumeServersByDiskType(0x0?, {0x0, 0x0}, 0x13?, {0x0?, 0x0, 0x0}, 0xc000101c00?, {0xc000bc6c60, 0x8}, ...)
	/Users/tochka/GolandProjects/seaweedfs/weed/shell/command_volume_balance.go:135 +0x16c
github.com/chrislusf/seaweedfs/weed/shell.balanceVolumeServers(0x42?, {0xc000f7b190?, 0x1, 0x1?}, 0x40d625?, {0x0, 0x0, 0x0}, 0x38?, {0xc000bc6c60, ...}, ...)
	/Users/tochka/GolandProjects/seaweedfs/weed/shell/command_volume_balance.go:115 +0xfc
github.com/chrislusf/seaweedfs/weed/shell.(*commandVolumeBalance).Do(0xc00031b7eb?, {0xc000789540, 0x2, 0x2}, 0xc0005aa120?, {0x2bca780, 0xc00000e018})
	/Users/tochka/GolandProjects/seaweedfs/weed/shell/command_volume_balance.go:95 +0x672
github.com/chrislusf/seaweedfs/weed/shell.processEachCmd(0xc0005b60a0?, {0xc00031b7d0, 0x1f}, 0xc0005aa120?)
	/Users/tochka/GolandProjects/seaweedfs/weed/shell/shell_liner.go:135 +0x3a7
github.com/chrislusf/seaweedfs/weed/shell.RunShell({0xc0006b7f30, {0x2bc8b00, 0xc00011b758}, {0x0, 0x0}, 0x0, 0xc0006b7f40, {0xc0000546a8, 0x14}, {0x2bb6a64, ...}})
	/Users/tochka/GolandProjects/seaweedfs/weed/shell/shell_liner.go:104 +0x548
github.com/chrislusf/seaweedfs/weed/command.runShell(0x3e17b38?, {0xc00004c050?, 0x0?, 0x0?})
	/Users/tochka/GolandProjects/seaweedfs/weed/command/shell.go:60 +0x2f8
main.main()
	/Users/tochka/GolandProjects/seaweedfs/weed/weed.go:81 +0x383