Fix condition for threshold-skipping

[primenumber]

What this patch does to fix the issue.

Quantized convolution output is used both non-quantizer and quantizer operations, optimizer optimize network wrongly.
pseudo code:

a = qconv(in, w)
b = quantize(a)
c = avgpool(a)

optimizer modify network to:

b = qconv_with_threshold_skipping(in, w)
c = avgpool(b) # Error!

This PR fix optimizer to stop apply threshold skipping if qconv or following operations until quantizer has multiple output operations.

Link to any relevant issues or pull requests.

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[iizukak]

OA

[iizukak]

/ready

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Readability Approval

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/ready

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