JENKINS-34667 Provision attempt is made when possible slaves count is 0.

src/main/java/hudson/plugins/ec2/EC2Cloud.java

@@ -490,7 +490,7 @@ private synchronized EC2AbstractSlave provisionSlaveIfPossible(SlaveTemplate tem
          * allocated, we don't look at that instance as available for provisioning.
          */
         int possibleSlavesCount = getPossibleNewSlavesCount(template);
-        if (possibleSlavesCount < 0) {
+        if (possibleSlavesCount <= 0) {
             LOGGER.log(Level.INFO, "Cannot provision - no capacity for instances: " + possibleSlavesCount);
             return null;
         }