ConfigurationRoot.GetChildren() never finishes if a configuration key starts with colon

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If a configuration key starts with :, ConfigurationRoot.GetChildrenImplementation() generates an infinite Linq query. This is because a key named e.g. :foo is read as <empty>:foo, which creates a ConfigurationSection with Path = "". ConfigurationSection in turn calls GetChildrenImplementation(Path) in order to traverse it's own children, but because it's Path property is set to "", the call is the same as the one made by ConfigurationRoot.GetChildren(), this causing an infinite loop.