GroupReference neglects parent node's path

[k3zi]

Xcodeproj/lib/xcodeproj/workspace/group_reference.rb

Line 57 in e008997

location = location_array[1] || ''

The same treatment that was done for FileReferences in: #633 needs to be considered for GroupReferences since groups can be nested in sub groups that use relative paths.

This can cause miscalculations like skipping over the parent group's folder while outputting the absolute file path.

Here is an example structure that would cause this:

<?xml version="1.0" encoding="UTF-8"?>
<Workspace
   version = "1.0">
   <Group
      location = "group:MyGroup"
      name = "MyGroup">
      <Group
         location = "group:MyRelativeToGroupSubGroup"
         name = "MyRelativeToGroupSubGroup">
         <FileRef
            location = "group:Project1/Project1.xcodeproj">
         </FileRef>

where Project1 is located at /path/to/workspace/MyGroup/MyRelativeToGroupSubGroup/Project1.xcodeproj. However FileReference.absolute_path now returns /path/to/workspace/MyRelativeToGroupSubGroup/Project1.xcodeproj