runtime: SetCPUProfileRate(0) crashes if profiler is already off

[emidoots]

What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.
1. Call runtime.SetCPUProfileRate(0) *with* the profiler already off (I.e. no previous
calls to runtime.SetCPUProfileRate).
2. A crash due to nil pointer dereference occurs.
3. Example (also happens on playground): http://play.golang.org/p/whHf24PCI5

What is the expected output?
The program should run without crashing.

What do you see instead?
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x4052ca]

goroutine 1 [running]:
runtime.panic(0x4ab880, 0x5a1d48)
    /home/stephen/go/src/pkg/runtime/panic.c:264 +0xb6
main.main()
    /home/stephen/Desktop/godev/src/code.google.com/p/goprof/cmd/goprof/goprof.go:24 +0x2e


Which compiler are you using (5g, 6g, 8g, gccgo)?
6g

Which operating system are you using?
I tested the same program and it crashed on the playground as well as my personal
linux/amd64 and windows/amd64 intel i7 machine.

Which version are you using?  (run 'go version')
Tip in both test cases - go version devel +36d5461843ce

Please provide any additional information below.

Maybe a test should be added for this too; since I think runtime/pprof is the only
client who uses this function in the standard library? I'm not sure.

[ceh]

Comment 1:

https://golang.org/cl/47950043

[ianlancetaylor]

Comment 2:

This issue was closed by revision aeeda70.

Status changed to Fixed.