reflect: fix isRegularMemory at case Array

[callthingsoff]

To match cmd/compile/internal/compare.IsRegularMemory,
this CL adds code for empty arrays of comparable element type.

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from qiulaidongfeng:

Patch Set 1: Code-Review+1 Run-TryBot+1

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Patch Set 1:

(1 comment)

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Message from Gopher Robot:

Patch Set 1: TryBot-Result+1

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Message from Jes Cok:

Patch Set 1:

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Message from Keith Randall:

Patch Set 1: Code-Review+2

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Message from Keith Randall:

Patch Set 1: Code-Review+1

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Message from Cherry Mui:

Patch Set 1: Code-Review+2

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This PR is being closed because golang.org/cl/558155 has been merged.