error creating GroovyPagesException if nested exception has no stack trace

GroovyPageView#createGroovyPageException(..) expects the exception that it is building around to have a stack trace. [It is possible for an exception not to have a stack trace](https://plumbr.io/blog/java/on-a-quest-for-missing-stacktraces). This causes a problem in the following code:
```
StackTraceElement[] stackTrace = exception.getStackTrace();
String className = stackTrace[0].getClassName();
```

Stack trace:
```
java.lang.ArrayIndexOutOfBoundsException: 0
at org.grails.web.servlet.view.GroovyPageView.createGroovyPageException(GroovyPageView.java:118)
at org.grails.web.servlet.view.GroovyPageView.handleException(GroovyPageView.java:112)
at org.grails.web.servlet.view.GroovyPageView.renderTemplate(GroovyPageView.java:80)
at org.grails.web.servlet.view.AbstractGrailsView.renderWithinGrailsWebRequest(AbstractGrailsView.java:71)
at org.grails.web.servlet.view.AbstractGrailsView.renderMergedOutputModel(AbstractGrailsView.java:55)
at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
at org.grails.web.sitemesh.GrailsLayoutView.renderInnerView(GrailsLayoutView.java:150)
at org.grails.web.sitemesh.GrailsLayoutView.obtainContent(GrailsLayoutView.java:128)
at org.grails.web.sitemesh.GrailsLayoutView.renderTemplate(GrailsLayoutView.java:63)
at org.grails.web.servlet.view.AbstractGrailsView.renderWithinGrailsWebRequest(AbstractGrailsView.java:71)
at org.grails.web.servlet.view.AbstractGrailsView.renderMergedOutputModel(AbstractGrailsView.java:55)
at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1286)
at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1041)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:984)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
...

```
### Steps to Reproduce

This is not an easily reproducible bug.

### Expected Behaviour

I expect to see the original error in my log files or on an error page.

### Actual Behaviour

The log files contain a stack trace from the process of creating a nesting exception, losing the context of the underlying problem.

### Environment Information

- **Operating System**: Centos 6.9
- **Grails Version:** 3.2.1
- **JDK Version:** Oracle 1.8.0_171
- **Container Version (If Applicable):** n/a

Start in GroovyPageView.java at createGroovyPageException, especially the stackTrace lookup at line 118. Inspect how an exception with no stack trace is handled and verify that the original error context is preserved instead of producing the reported ArrayIndexOutOfBoundsException.

Written by the indexing model from the issue text.