Workaround for panic: weird mapping Exec

[bozaro]

Workaround for errors like:

panic: weird mapping Exec

goroutine 1 [running]:
golang.org/x/debug/internal/gocore.(*Process).readSpans(0xc0003322c0, 0xc0003322c0, 0xa58f780, 0xc00e328d20, 0xc00fa6c000, 0x4b, 0x80)
	/home/bozaro/github/debug/internal/gocore/process.go:316 +0x304e
golang.org/x/debug/internal/gocore.(*Process).readHeap(0xc0003322c0)
	/home/bozaro/github/debug/internal/gocore/process.go:272 +0x77b
golang.org/x/debug/internal/gocore.Core(0xc00016e000, 0x40, 0x0, 0x0)
	/home/bozaro/github/debug/internal/gocore/process.go:157 +0x2c4
main.readCore(0xc000167d50, 0xc000167ce0, 0x783174, 0xc00011edc0)
	/home/bozaro/github/debug/cmd/viewcore/main.go:265 +0xd2
main.runRead(0xc51f60, 0xc000064de0, 0x1, 0x1)
	/home/bozaro/github/debug/cmd/viewcore/main.go:719 +0x34
github.com/spf13/cobra.(*Command).execute(0xc51f60, 0xc000064da0, 0x1, 0x1, 0xc51f60, 0xc000064da0)
	/home/bozaro/go/pkg/mod/github.com/spf13/cobra@v0.0.3/command.go:766 +0x29d
github.com/spf13/cobra.(*Command).ExecuteC(0xc507a0, 0x8c0862, 0x1, 0xc000167f00)
	/home/bozaro/go/pkg/mod/github.com/spf13/cobra@v0.0.3/command.go:852 +0x2ea
github.com/spf13/cobra.(*Command).Execute(...)
	/home/bozaro/go/pkg/mod/github.com/spf13/cobra@v0.0.3/command.go:800
main.main()
	/home/bozaro/github/debug/cmd/viewcore/main.go:243 +0x104

Dump was generated by binary compiled with Go 1.13.9.

[gopherbot]

This PR (HEAD: de2d498) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/debug/+/240898 to see it.

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[gopherbot]

Message from Keith Randall:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Artem Navrotskiy:

Patch Set 1:

(1 comment)

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After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Bryan Boreham:

Patch Set 1:

(1 comment)

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After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Daniel Martí:

Patch Set 1: Trust+1

(1 comment)

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After addressing review feedback, remember to publish your drafts!