Issue #3291904 by quietone, Spokje: Create a test for a dev release without a date

Closes #3291904

core/modules/update/tests/fixtures/release-history/drupal.dev-no-date.xml

+<?xml version="1.0" encoding="utf-8"?>
+<project xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <title>Drupal</title>
+  <short_name>drupal</short_name>
+  <dc:creator>Drupal</dc:creator>
+  <supported_branches>8.0.,8.1.</supported_branches>
+  <project_status>published</project_status>
+  <link>http://example.com/project/drupal</link>
+  <terms>
+    <term><name>Projects</name><value>Drupal project</value></term>
+  </terms>
+  <releases>
+    <release>
+      <name>Drupal 8.1.x-dev</name>
+      <version>8.1.x-dev</version>
+      <status>published</status>
+      <release_link>http://example.com/drupal-8-1-x-dev-release</release_link>
+      <download_link>http://example.com/drupal-8.1.x-dev.tar.gz</download_link>
+      <terms>
+        <term><name>Release type</name><value>Bug fixes</value></term>
+      </terms>
+    </release>
+  </releases>
+</project>