Do not show stack trace on missing commit

A missing commit message is not sufficient to justify the distraction
of a stack trace in the log.  State that the commit message cannot be
displayed because the commit cannot be found.

src/main/java/hudson/plugins/git/GitSCM.java

@@ -1426,7 +1426,9 @@ private void printCommitMessageToLog(TaskListener listener, GitClient git, final
         try {
             RevCommit commit = git.withRepository(new RevCommitRepositoryCallback(revToBuild));
             listener.getLogger().println("Commit message: \"" + commit.getShortMessage() + "\"");
-        } catch (InterruptedException | MissingObjectException e) {
+        } catch (MissingObjectException e) {
+            listener.getLogger().println("Commit '" + e.getObjectId() + "' not found - no commit message to print");
+        } catch (InterruptedException e) {
             e.printStackTrace(listener.error("Unable to retrieve commit message"));
         }
     }