#### Describe the bug
The irrelevant error returned when requesting illegal URL, like: "tel:484-695-3408"
```
TypeError: Cannot read property 'replace' of null
    at dispatchHttpRequest (node_modules/axios/lib/adapters/http.js:109:74)
    at new Promise (<anonymous>)
    at httpAdapter (node_modules/axios/lib/adapters/http.js:46:10)
    at dispatchRequest (node_modules/axios/lib/core/dispatchRequest.js:52:10)
```

#### To Reproduce
```js
axios.get('tel:484-695-3408').catch(err => console.error(err));
```

#### Expected behavior
Return descriptive error, like "Unsupported protocol tel:"

#### Environment
 - Axios Version: 0.21.1
 - Adapter: HTTP
 - Browser: none
 - Browser Version: none
 - Node.js Version: 12.19.0
 - OS: MacOS 10.14
 - Additional Library Versions: none

#### Additional context/Screenshots
none
lib/adapters/xhr.js
'use strict';
var utils = require('./../utils');
var settle = require('./../core/settle');
var cookies = require('./../helpers/cookies');
var buildURL = require('./../helpers/buildURL');
var buildFullPath = require('../core/buildFullPath');
var parseHeaders = require('./../helpers/parseHeaders');
var isURLSameOrigin = require('./../helpers/isURLSameOrigin');
var createError = require('../core/createError');
var transitionalDefaults = require('../defaults/transitional');
var Cancel = require('../cancel/Cancel');
module.exports = function xhrAdapter(config) {
  return new Promise(function dispatchXhrRequest(resolve, reject) {
    var requestData = config.data;
    var requestHeaders = config.headers;
    var responseType = config.responseType;
    var onCanceled;
    function done() {