EA-226344 - do not show JdkDownloader dialog if no items were found in the list

It is a rare case we have no items in the feed. It is most likely caused by a MITM proxy or anything that corrupts our jdks.json

GitOrigin-RevId: ae9915f1065543966780a585f7003e69160c90a0

platform/lang-impl/src/com/intellij/openapi/projectRoots/impl/jdkDownloader/JdkDownloader.kt

@@ -44,6 +44,16 @@ internal class JdkDownloader : SdkDownload, JdkDownloaderBase {
     } ?: return
 
     if (project?.isDisposed == true) return
+
+    if (items.isEmpty()) {
+      Messages.showMessageDialog(project,
+                                 "No JDK packages are available for download",
+                                 JdkDownloadDialog.DIALOG_TITLE,
+                                 Messages.getErrorIcon()
+      )
+      return
+    }
+
     val (jdkItem, jdkHome) = JdkDownloadDialog(project, parentComponent, sdkTypeId, items).selectJdkAndPath() ?: return
 
     /// prepare the JDK to be installed (e.g. create home dir, write marker file)