Bugfix #17913

Bah... fix for envmaps just before 2.48 release gave good looking envmaps 
only when there was no sky involved...

The alpha in environment maps should be reset to 255... something that was 
never done before, but also didn't show errors until other fixes in image 
rendering were done.

source/blender/render/intern/source/envmap.c

@@ -439,12 +439,19 @@ static void render_envmap(Render *re, EnvMap *env)
 
 		if(re->test_break()==0) {
 			RenderLayer *rl= envre->result->layers.first;
+			int y;
+			char *alpha;
 			
 			ibuf= IMB_allocImBuf(envre->rectx, envre->recty, 24, IB_rect, 0);
 			ibuf->rect_float= rl->rectf;
 			IMB_rect_from_float(ibuf);
 			ibuf->rect_float= NULL;
-				
+			
+			/* envmap renders without alpha */
+			alpha= ((char *)ibuf->rect)+3;
+			for(y= ibuf->x*ibuf->y - 1; y>=0; y--, alpha+=4)
+				*alpha= 255;
+			
 			env->cube[part]= ibuf;
 		}