api-extractor: check whether folder has a package.json

Often when switching between branches, I have empty folders in my working copy and Git doesn't track folders. Another case is the now deleted `core` package which remains as an empty folder locally (due to the node_modules folder still being there).
Sadly, api-extractor crashes on empty folder, so this introduces a check that the folder is a package by checking for the package.json file.

Signed-off-by: Oliver Sand <oliver.sand@sda-se.com>

scripts/api-extractor.ts

@@ -21,6 +21,7 @@ import {
   resolve as resolvePath,
   relative as relativePath,
   dirname,
+  join,
 } from 'path';
 import fs from 'fs-extra';
 import {
@@ -96,6 +97,13 @@ async function findPackageDirs() {
         continue;
       }
 
+      try {
+        const packageJsonPath = join(fullPackageDir, 'package.json');
+        await fs.access(packageJsonPath);
+      } catch (_) {
+        continue;
+      }
+
       const packageDir = relativePath(projectRoot, fullPackageDir);
       if (!SKIPPED_PACKAGES.includes(packageDir)) {
         packageDirs.push(packageDir);