GetPatch: Fix NullPointerException

On close 'bin' may be null. This problem was introduced by change
I37d7cb29c.

java.lang.NullPointerException
  at com.google.gerrit.server.restapi.change.GetPatch.apply(GetPatch.java:139)
  at com.google.gerrit.server.restapi.change.GetPatch.apply(GetPatch.java:43)
  at com.google.gerrit.httpd.restapi.RestApiServlet.lambda$invokeRestReadViewWithRetry$6(RestApiServlet.java:792)
  at com.github.rholder.retry.AttemptTimeLimiters$NoAttemptTimeLimit.call(AttemptTimeLimiters.java:78)
  at com.github.rholder.retry.Retryer.call(Retryer.java:160)
  at com.google.gerrit.server.update.RetryHelper.executeWithTimeoutCount(RetryHelper.java:560)
  at com.google.gerrit.server.update.RetryHelper.execute(RetryHelper.java:503)
  at com.google.gerrit.server.update.RetryableAction.call(RetryableAction.java:172)
  at com.google.gerrit.httpd.restapi.RestApiServlet.invokeRestEndpointWithRetry(RestApiServlet.java:883)
  at com.google.gerrit.httpd.restapi.RestApiServlet.invokeRestReadViewWithRetry(RestApiServlet.java:787)
  at com.google.gerrit.httpd.restapi.RestApiServlet.service(RestApiServlet.java:507)
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
  ...

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: Iebdb0506ebd097978ccd512e90cc7e3efbd1913e

java/com/google/gerrit/server/restapi/change/GetPatch.java

diff --git a/java/com/google/gerrit/server/restapi/change/GetPatch.java b/java/com/google/gerrit/server/restapi/change/GetPatch.java
index 31785be..66ccef3 100644
--- a/java/com/google/gerrit/server/restapi/change/GetPatch.java
+++ b/java/com/google/gerrit/server/restapi/change/GetPatch.java
@@ -136,7 +136,9 @@
       } finally {
         if (close) {
           rw.close();
-          bin.close();
+          if (bin != null) {
+            bin.close();
+          }
         }
       }
     } finally {