tr_image: make the $black builtin image opaque

Author: illwieckz

src/engine/renderer/tr_image.cpp

@@ -2652,7 +2652,7 @@ void R_CreateBuiltinImages()
 	tr.whiteImage = R_CreateImage( "$white", ( const byte ** ) &dataPtr, 1, 1, 1, imageParams );
 
 	// we use a solid black image instead of disabling texturing
-	memset( data, 0, sizeof( data ) );
+	Vector4Set( data, 0, 0, 0, 255 );
 
 	tr.blackImage = R_CreateImage( "$black", ( const byte ** ) &dataPtr, 1, 1, 1, imageParams );
 

src/engine/renderer/tr_local.h

@@ -2445,7 +2445,7 @@ enum
 		image_t    *defaultImage;
 		image_t    *cinematicImage[ MAX_IN_GAME_VIDEOS ];
 		image_t    *whiteImage; // full of 0xff
-		image_t    *blackImage; // full of 0x0
+		image_t    *blackImage; // 0x0 color channels, 0xff alpha channel
 		image_t    *redImage;
 		image_t    *greenImage;
 		image_t    *blueImage;