Don't print critical path parallelism ratio if elapsed time is 0.

Test: m nothing, examine out/soong.log
Change-Id: Ib23902c703d306337b2a5150d6d63b1e3d0f95b3

ui/status/critical_path.go

@@ -112,8 +112,10 @@ func (cp *criticalPath) Flush() {
 		if !cp.start.IsZero() {
 			elapsedTime := cp.end.Sub(cp.start).Round(time.Second)
 			cp.log.Verbosef("elapsed time %s", elapsedTime.String())
-			cp.log.Verbosef("perfect parallelism ratio %d%%",
-				int(float64(criticalTime)/float64(elapsedTime)*100))
+			if elapsedTime > 0 {
+				cp.log.Verbosef("perfect parallelism ratio %d%%",
+					int(float64(criticalTime)/float64(elapsedTime)*100))
+			}
 		}
 		cp.log.Verbose("critical path:")
 		for i := len(criticalPath) - 1; i >= 0; i-- {