fix(gatsby-source-filesystem): guard against null pathname in getParsedPath

[funsaized]

Summary

Fixes #39532

getParsedPath in gatsby-source-filesystem/src/utils.js calls path.parse(Url.parse(url).pathname) without a null fallback. For malformed or edge-case URL inputs where Url.parse(url).pathname returns null, path.parse throws a TypeError, crashing callers like getRemoteFileExtension and getRemoteFileName.

Changes

• Added || '' fallback to Url.parse(url).pathname in getParsedPath, matching the existing guard in the TypeScript equivalent at gatsby-core-utils/src/filename-utils.ts (line 12)
• Added test case verifying that empty strings and mailto: URLs no longer throw

Before

function getParsedPath(url) {
  return path.parse(Url.parse(url).pathname)  // throws TypeError when pathname is null
}

After

function getParsedPath(url) {
  return path.parse(Url.parse(url).pathname || ``)  // safe fallback, matches gatsby-core-utils
}