Fix corrupted frames producing by fog glare node

Seems to be simple non-initialized buffer used in math, but additional
check would be welcome here.

At least now result doesn't seems to be corrupted and seems to behaving
the same way as non-tile compositor.

source/blender/compositor/operations/COM_GlareFogGlowOperation.cpp

@@ -260,6 +260,7 @@ void convolve(float *dst, MemoryBuffer *in1, MemoryBuffer *in2)
 	float *imageBuffer = in1->getBuffer();
 
 	MemoryBuffer *rdst = new MemoryBuffer(NULL, in1->getRect());
+	memset(rdst->getBuffer(), 0, rdst->getWidth() * rdst->getHeight() * COM_NUMBER_OF_CHANNELS * sizeof(float));
 
 	// convolution result width & height
 	w2 = 2 * kernelWidth - 1;