Closes #90: eqPly: Crash with direct send and 30 GPUs

This was a race introduced by #82:

[rcv thread]
_handleData:
  dispatchCommand to instance1
    enqueue to foo thread

[foo thread]
  process command
  release command

[rcv thread]
  dispatch the same command to instance2
    cloneCommand
      compact cache
      free command [yee-ha!]

Fix by retaining the command during dispatch.

[ ] May break build
[ ] May break existing applications (see CHANGES.txt)
[x] Bugfix
[ ] New Feature
[ ] Cleanup
[ ] Optimization
[ ] Documentation

libs/co/localNode.cpp

@@ -1064,14 +1064,16 @@ Command& LocalNode::allocCommand( const uint64_t size )
 void LocalNode::_dispatchCommand( Command& command )
 {
     EQASSERT( command.isValid( ));
+    command.retain();
 
-    const bool dispatched = dispatchCommand( command );
-
-    _redispatchCommands();
-
-    if( !dispatched )
+    if( dispatchCommand( command ))
+    {
+        command.release();
+        _redispatchCommands();
+    }
+    else
     {
-        command.retain();
+        _redispatchCommands();
         _pendingCommands.push_back( &command );
     }
 }