[Fix] importType: avoid crashing on a non-string

[lencioni]

While writing imports in VSCode recently, I started to get errors throwm
from eslint that appear to originate from eslint-plugin-import.

Here's the strack trace from the output panel:

[Error - 3:52:43 PM] TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received undefined
    at validateString (internal/validators.js:124:11)
    at isAbsolute (path.js:1029:5)
    at isAbsolute (/path/to/repo/node_modules/eslint-plugin-import/src/core/importType.js:17:10)
    at typeTest (/path/to/repo/node_modules/eslint-plugin-import/src/core/importType.js:92:7)
    at resolveImportType (/path/to/repo/node_modules/eslint-plugin-import/src/core/importType.js:105:10)
    at reportIfMissing (/path/to/repo/node_modules/eslint-plugin-import/src/rules/no-extraneous-dependencies.js:170:7)
    at commonjs (/path/to/repo/node_modules/eslint-plugin-import/src/rules/no-extraneous-dependencies.js:267:7)
    at checkSourceValue (/path/to/repo/node_modules/eslint-module-utils/moduleVisitor.js:29:5)
    at checkSource (/path/to/repo/node_modules/eslint-module-utils/moduleVisitor.js:34:5)
    at /path/to/repo/node_modules/eslint/lib/linter/safe-emitter.js:45:58

I am able to trigger this consistently when writing an import, before I
start the open quote, like this:

import foo from

I found #1931
which pointed at a problem in the resolvers causing this problem. We do
use some custom resolvers with this plugin, so I tried disabling that
but the problem persisted.

Thankfully, I was able to reproduce this error in the test suite.

It would be good if this plugin handled this scenario gracefully instead
of throwing an error.

[ljharb]

I don't think it's possible to have a test here, since this is invalid syntax, so eslint can't parse it. That said, I can repurpose this into a bug fix given that stack trace, thanks!

[codecov]

Codecov Report

Merging #2305 (e8794f1) into main (7c239fe) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2305   +/-   ##
=======================================
  Coverage   94.64%   94.64%           
=======================================
  Files          65       65           
  Lines        2691     2691           
  Branches      891      891           
=======================================
  Hits         2547     2547           
  Misses        144      144           

Impacted Files	Coverage Δ
src/core/importType.js	100.00% <ø> (ø)
src/rules/no-absolute-path.js	100.00% <100.00%> (ø)

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