Exit abnormally when multiple SYNTH_START commands are posted

[iRi-E]

When two SYNTH_START commands are successively posted to the same model, if the second one is received before SYNTH_EVENT_START for the first one is emitted, QMAOpenJTalkPlugin shuts down and QtMMDAI crashes.

In this case I get error messages like bellow:

WARNING: JPCommonLabel_push_word() in jpcommon_label.c: First mora should not be short pause.
WARNING: JPCommonLabelPhoneme_convert_unvoice() in jpcommon_label.c: U cannot be unvoiced.

Error: HTS_Label_load_from_fp: label list is not initialized.
セグメンテーション違反です
$

It seems that QMAOpenJTalkPlugin::run() is not thread-safe. I think this function needs mutual exclusion.

[iRi-E]

I wrote a patch for this bug:

https://gist.github.com/961258

I implemented the mutual exclusion by using QMutex class.