Merge pull request #1678 from stephenc/jenkins-28115

[FIXED JENKINS-28115] Division by zero in Executor.getProgress()

core/src/main/java/hudson/model/Executor.java

@@ -642,7 +642,7 @@ public class Executor extends Thread implements ModelObject {
         } finally {
             lock.readLock().unlock();
         }
-        if (d < 0) {
+        if (d <= 0) {
             return -1;
         }