fix crashers with wifi/virtual displays

    Source source = fbSourceForCompositionType(mCompositionType);

    if (source == SOURCE_SINK) {

        if (mOutputProducerSlot < 0) {

            // Last chance bailout if something bad happened earlier. For example,

            // in a GLES configuration, if the sink disappears then dequeueBuffer

            // will fail, the GLES driver won't queue a buffer, but SurfaceFlinger

            // will soldier on. So we end up here without a buffer. There should

            // be lots of scary messages in the log just before this.

            VDS_LOGE("dequeueBuffer: no buffer, bailing out");

            return NO_MEMORY;

        }

        // We already dequeued the output buffer. If the GLES driver wants

        // something incompatible, we have to cancel and get a new one. This

        // will mean that HWC will see a different output buffer between

        hwc.commit();

    }

    // make the default display current because the VirtualDisplayDevice code cannot

    // deal with dequeueBuffer() being called outside of the composition loop; however

    // the code below can call glFlush() which is allowed (and does in some case) call

    // dequeueBuffer().

    getDefaultDisplayDevice()->makeCurrent(mEGLDisplay, mEGLContext);

    for (size_t dpy=0 ; dpy<mDisplays.size() ; dpy++) {

        sp<const DisplayDevice> hw(mDisplays[dpy]);

        const Vector< sp<Layer> >& currentLayers(hw->getVisibleLayersSortedByZ());