Fix for #851: do not close system ClassLoader

or any other not created by GroovyClassLoaderFactory

base/org.eclipse.jdt.groovy.core/src/org/codehaus/jdt/groovy/internal/compiler/GroovyClassLoaderFactory.java

@@ -5,7 +5,7 @@
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
+ *     https://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
@@ -88,8 +88,7 @@ private static void close(ClassLoader classLoader) {
         }
         if (classLoader instanceof GroovyClassLoader) {
             ((GroovyClassLoader) classLoader).clearCache();
-        }
-        if (classLoader.getParent() instanceof URLClassLoader) {
+            // parent was created by newClassLoader(...)
             close(classLoader.getParent());
         }
     }