Bufix #1942

Halos with Flare option didn't render correct in Unified render, they were
added twice!
Also noticed errors in applying alpha for 'Premul' alpha in Unified. Fixed.

source/blender/render/intern/source/pixelshading.c

@@ -395,6 +395,11 @@ void renderSkyPixelFloat(float x, float y)
 	switch (keyingType) {
 	case RE_ALPHA_PREMUL:
 		/* Premul: don't fill, and don't change the values! */
+		collector[0] = 0.0; 
+		collector[1] = 0.0; 
+		collector[2] = 0.0; 
+		collector[3] = 0.0; 
+		break;
 	case RE_ALPHA_KEY:
 		/*
 		  Key: Leave pixels fully coloured, but retain alpha data, so you   

source/blender/render/intern/source/vanillaRenderPipe.c

@@ -262,8 +262,6 @@ void zBufShadeAdvanced()
 			 R.r.edgeR, R.r.edgeG, R.r.edgeB);
 	}
 
-	add_halo_flare(); /* from rendercore */
-	
 	if (!(R.r.mode & R_OSA)) {
 		jit[0][0] = xjit;
 		jit[0][1] = yjit;