Catch exception with duplicate username/email

Description

Previously, there was no catch for the AccountValidationError
exception raised by the account creation function. If, for some
reason, the user made it past the first check for a duplicate
username/email, then the exception was raised, uncaught, and
crashed the server.

CC: @stvstnfrd

Done

Assignee

Unassigned

Reporter

Open Source Pull Request Bot

Contributor Name

Po Tsui

Repo

edx/edx-platform

Customer

None

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edX Theme

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edX Squad

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Github Lines Deleted

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Priority

Unset