INT-3433 More Polishing

If the assembler couldn't execute a new assembler after assembling
the current message (when it detected there is more data), in the
finally block it would "continue" only if the socket was still
open.

The test case closes the socket after sending 4 messages so when
this condition occurred, the assembler failed to continue and
data was left in the buffer.

Remove the `isOpen()` check in the finally block and always continue
if there's not another assembler running and there's data available.