Fix data race in MultiProgressMonitor

This is work related to [1] but AFAICT real race condition happens only
for count member. Therefore proposed protecting it in this change.

[1] https://gerrit-review.googlesource.com/#/c/87442/
Change-Id: I8eca2e17be83af25cffd30b4de40cf7f46eb6f48
Signed-off-by: Jacek Centkowski <geminica.programs@gmail.com>

gerrit-server/src/main/java/com/google/gerrit/server/git/MultiProgressMonitor.java

@@ -319,7 +319,7 @@ public class MultiProgressMonitor {
     if (!tasks.isEmpty()) {
       boolean first = true;
       for (Task t : tasks) {
-        int count = t.count;
+        int count = t.getCount();
         if (count == 0) {
           continue;
         }