Fix startup with gridfsbinaries template

ERROR [localhost-startStop-1] [org.nuxeo.runtime.model.impl.RegistrationInfoImpl] Failed to register extension to: service:org.nuxeo.ecm.core.blob.BlobManager, xpoint: configuration in component: service:org.nuxeo.gridfs.config
java.lang.NullPointerException
	at org.nuxeo.runtime.mongodb.MongoDBConnectionHelper.getDatabase(MongoDBConnectionHelper.java:92)
	at org.nuxeo.runtime.mongodb.MongoDBComponent.getDatabase(MongoDBComponent.java:128)
	at org.nuxeo.ecm.core.storage.mongodb.GridFSBinaryManager.initialize(GridFSBinaryManager.java:124)
	at org.nuxeo.ecm.core.blob.BlobManagerComponent.getBlobProvider(BlobManagerComponent.java:172)
	at org.nuxeo.ecm.core.blob.BlobManagerComponent.registerBlobProvider(BlobManagerComponent.java:126)
	at org.nuxeo.ecm.core.blob.BlobManagerComponent.registerContribution(BlobManagerComponent.java:103)
	at org.nuxeo.runtime.model.DefaultComponent.registerExtension(DefaultComponent.java:53)
	at org.nuxeo.runtime.model.impl.ComponentInstanceImpl.registerExtension(ComponentInstanceImpl.java:209)
	at org.nuxeo.runtime.model.impl.ComponentManagerImpl.registerExtension(ComponentManagerImpl.java:413)
	at org.nuxeo.runtime.model.impl.RegistrationInfoImpl.activate(RegistrationInfoImpl.java:439)
	at org.nuxeo.runtime.model.impl.ComponentManagerImpl.activateComponent(ComponentManagerImpl.java:547)
	at org.nuxeo.runtime.model.impl.ComponentManagerImpl.activateComponents(ComponentManagerImpl.java:524)
	at org.nuxeo.runtime.model.impl.ComponentManagerImpl.start(ComponentManagerImpl.java:787)
	at org.nuxeo.runtime.osgi.OSGiRuntimeService.startComponents(OSGiRuntimeService.java:460)
	at org.nuxeo.runtime.osgi.OSGiRuntimeService.frameworkEvent(OSGiRuntimeService.java:475)
	at org.nuxeo.osgi.OSGiAdapter.fireFrameworkEvent(OSGiAdapter.java:223)
	at org.nuxeo.osgi.application.loader.FrameworkLoader.doStart(FrameworkLoader.java:226)
	at org.nuxeo.osgi.application.loader.FrameworkLoader.start(FrameworkLoader.java:125)
	at org.nuxeo.runtime.deployment.NuxeoStarter.start(NuxeoStarter.java:120)
	at org.nuxeo.runtime.deployment.NuxeoStarter.contextInitialized(NuxeoStarter.java:93)
	at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4745)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5207)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
	at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:752)
	at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:728)
	at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
	at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:630)
	at org.apache.catalina.startup.HostConfig$DeployDescriptor.run(HostConfig.java:1842)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:748)