StashBuildTrigger: Use isBuildable() instead of isDisabled()

The job field should be set at the time of the check.

TODO: Test. What would happen if the trigger tries to start a disabled
job?

Author: proski

src/main/java/stashpullrequestbuilder/stashpullrequestbuilder/StashBuildTrigger.java

@@ -295,14 +295,13 @@ private List<ParameterValue> getDefaultParameters() {
 
   @Override
   public void run() {
-    if (stashPullRequestsBuilder == null) {
+    if (job == null || stashPullRequestsBuilder == null) {
       logger.info("Not ready to run.");
       return;
     }
 
-    AbstractProject project = stashPullRequestsBuilder.getProject();
-    if (project.isDisabled()) {
-      logger.fine(format("Project disabled, skipping build (%s).", project.getName()));
+    if (job.isBuildable()) {
+      logger.fine(format("Job is not buildable, skipping build (%s).", job.getName()));
       return;
     }