Update MINA SSHD to 0.5.1-r1031886

The new version contains a work-around for failed sftp connections,
resolving a common NullPointerException error in server error logs.

Change-Id: Iebe667e8cd81cb79848833e2a5de68447fcd42fa
Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshDaemon.java b/gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshDaemon.java
index 2636ff2..69dd170 100644
--- a/gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshDaemon.java
+++ b/gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshDaemon.java
@@ -58,8 +58,11 @@
 import org.apache.sshd.common.util.SecurityUtils;
 import org.apache.sshd.server.Command;
 import org.apache.sshd.server.CommandFactory;
+import org.apache.sshd.server.FileSystemFactory;
+import org.apache.sshd.server.FileSystemView;
 import org.apache.sshd.server.ForwardingFilter;
 import org.apache.sshd.server.PublickeyAuthenticator;
+import org.apache.sshd.server.SshFile;
 import org.apache.sshd.server.UserAuth;
 import org.apache.sshd.server.auth.UserAuthPublicKey;
 import org.apache.sshd.server.channel.ChannelDirectTcpip;
@@ -136,6 +139,7 @@
     initSignatures();
     initChannels();
     initForwardingFilter();
+    initFileSystemFactory();
     initSubsystems();
     initCompression();
     initUserAuth(userAuth);
@@ -485,4 +489,17 @@
       }
     });
   }
+
+  private void initFileSystemFactory() {
+    setFileSystemFactory(new FileSystemFactory() {
+      @Override
+      public FileSystemView createFileSystemView(String userName) {
+        return new FileSystemView() {
+          @Override
+          public SshFile getFile(String file) {
+            return null;
+          }};
+      }
+    });
+  }
 }
diff --git a/pom.xml b/pom.xml
index 9a4e2c1..0f59058 100644
--- a/pom.xml
+++ b/pom.xml
@@ -478,7 +478,7 @@
       <dependency>
         <groupId>org.apache.sshd</groupId>
         <artifactId>sshd-core</artifactId>
-        <version>0.4.0-r897374</version>
+        <version>0.5.1-r1031886</version>
       </dependency>
 
       <dependency>