Empty Trace

This is another trivial missing pattern that we need to add to make software log analysis pattern system complete. It ranges from a totally empty trace message list where only a meta-trace header (if any) describing overall trace structure is present to a few messages where we expect thousands. This is also an extreme case of Truncated Trace (Volume 5, page 301), No Activity (Volume 5, page 297) and Missing Component (Volume 4, page 342) patterns for a trace taken as a whole. Note, that an empty trace file doesn't necessarily have a zero file size because a tracing architecture may preallocate some file space for block data writing.