Fix validation in resource id parsing

[karataliu]

Thank you for your contribution to Go-AutoRest! We will triage and review it as soon as we can.

Before fix, 'ANYSTRING+valid id' can also be parsed as valid id, that's not correct.

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• I've tested my changes, adding unit tests if applicable.
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[jhendrixMSFT]

Can you please provide a brief description of what's broken without this fix?

[karataliu]

@jhendrixMSFT
That's in description, without the fix:
ABCDEF/subscription/xxx/resourcegroup/xxx/... is considered a valid id, but actually not.