trace-graph: Added some fixes for the trace labels
trace-graph: Added some fixes for the trace labels

The trace labels had some minor bugs, and one major one (would crash
if we zoomed in so far that a CPU line had no events).

Signed-off-by: Steven Rostedt <43232e92d70cc7aa53504ad0397085ee47bad87f@goodmis.org>

bigzz/trace-cmd,bigzz/trace-cmd