Don't create unnecessary RenderThread's instance when executing 'dumpsys gfxinfo'

To obtain the gfxinfo for each process, the static method of RenderProxy is used, which is named outputLogBuffer().
In there,
1. RenderTask is created for getting DisplayList Commands in RenderNode.
2. staticPostAndWait() is called
3. RenderThread's instance is created by 'RenderThread::getInstance()' in staticPostAndWait()

In case of the service, they don't use HW Acceleration, so don't need RenderThread.
But, by the process of No.3, RenderThread is created for all process.
As we know, RenderThread never be destroyed while the process is alive.
This patch checks RenderThread instance before the creation of RenderTask.
And, there is no one, just return to prevent the unnecessay creation of it.

Change-Id: I4fe29d83c9ced3e8b67177c0874c5d8ee62e1870