Don't panic if readdrivestat returns negative value

[VladRassokhin]

Context:
We observed several node_exporter panics on a machine which is used to create disk images.
Machine it could have more than 16 disks or add/remove them while readdrivestat is running, so some error in IOKit calls could arise.
That should not lead to a node_exporter failure though.

Here's an example panic log:

panic: runtime error: makeslice: len out of range

goroutine 188748 [running]:
github.com/lufia/iostat.ReadDriveStats(0x40741c0, 0xc0004c7d98, 0xf1b8b744, 0xc000081200, 0xc0004c7da8)
        github.com/lufia/iostat@v1.1.0/iostat_darwin.go:21 +0x86
github.com/prometheus/node_exporter/collector.(*diskstatsCollector).Update(0xc00028c330, 0xc000330b40, 0x4b04200, 0xc00023e1c0)
        github.com/prometheus/node_exporter/collector/diskstats_darwin.go:190 +0x34
github.com/prometheus/node_exporter/collector.execute(0x46d28ac, 0x9, 0x478d080, 0xc00028c330, 0xc000330b40, 0x478ce80, 0xc0001afbc0)
        github.com/prometheus/node_exporter/collector/collector.go:153 +0x84
github.com/prometheus/node_exporter/collector.NodeCollector.Collect.func1(0xc000330b40, 0xc0001afe60, 0x478ce80, 0xc0001afbc0, 0xc0003a13b0, 0x46d28ac, 0x9, 0x478d080, 0xc00028c330)
        github.com/prometheus/node_exporter/collector/collector.go:144 +0x71
created by github.com/prometheus/node_exporter/collector.NodeCollector.Collect
        github.com/prometheus/node_exporter/collector/collector.go:143 +0x13c

[lufia]

16 disks! great!

[VladRassokhin]

16 disks! great!

Most of that disks are virtual, also problem could be in other place. Anyway program should not panic in such case.

[lufia]

@VladRassokhin thanks. I will release new version soon.

[lufia]

released: https://pkg.go.dev/github.com/lufia/iostat@v1.1.1

[VladRassokhin]

Thank you!