Fix sending object info in MTP stack.

This CL fixes three bugs:
1. Wrong condition, which caused MtpDevice::sendData always return false.
2. Sending data separately was incompatible with the server side, causing
   receiving only partial data on the server side.
3. Sending uninitialized buffers (sic!) from MtpDevice::sendObjectInfo
   due to missing call to reset().
4. Sending corrupted packets from MtpDevice::sendObjectInfo (shifted by
   4 bytes) due to missing reset().
5. Sending incorrect parent in MtpDevice::sendObjectInfo in case of not
   specified parent.

Change-Id: Ia545c66b388ea9a292ba31f6ff034e2467037d92