fix: read property error of undefined when DOMException occured

[dreamdevil00]

What type of issue are you creating?

• Bug
• Enhancement
• Question

What version of this module are you using?

• 2.0.10 (Stable)
• 2.1.0-rc.n (2.1 Release Candidate n)
• Other

Write other if any:

Please add a description for your issue:

I passed a wrong baseUrl to config accidently

const baseUrl = window.location.host;
LoopBackConfig.setBaseUrl(baseUrl);

when I call api, an DOMException error occured, and report the error as title.
The DOMException error message is

DOMException: Failed to execute 'open' on 'XMLHttpRequest': Invalid URL

Related code:
LINK

we should make sure errorResponse.error exists, PTAL