Handle possible division by zero in _calc_p (#15)

This fixes ZeroDivisionError raised by _calc_timeline when the last
rendered template is measured to take 0.0 seconds (i.e. its 'start' is
equal to its 'end'). In this case, we get self.t_max == start == end,
and we divide by zero when calculating rel_duration_p.

Author: micjabbour

template_profiler_panel/panels/template.py

@@ -129,7 +129,8 @@ def disable_instrumentation(self):
         self.is_enabled = False
 
     def _calc_p(self, part, whole):
-        return (part / whole) * 100.0
+        # return the percentage of part or 100% if whole is zero
+        return (part / whole) * 100.0 if whole else 100.0
 
     def _calc_timeline(self, start, end):
         result = {}