[TxMt] [TM2] TM2 hangs when calling `mate` without arguments from inside TM2

[Martin Kühl]

To reproduce, enter the following text on a new line, then hit ^r
    "$TM_SUPPORT_PATH/bin/mate"

TextMate will open a new untitled tab, then become
unresponsive. However, the OS won't mark it as unresponsive in the Force
Quit dialog.

Tested with r9015 and r9028.

Cheers,
Martin