dri: Do not create DRI2 buffers for unrecognized DRI2 buffer tokens

Before this commit, if a client were to request an unrecognized DRI2
buffer, such as DRI2BufferStencil, then I830DRI2CreateBuffer() allocated
and returned an X-tiled buffer by accident. The problem was that
unrecognized tokens were caught by the default case of a switch statement.

Now, when given unrecognized DRI2 tokens, I830DRI2CreateBuffers() returns
null.

This shouldn't break older Mesa versions, because they never query (via
DRI2GetBuffersWithFormat) for the drawable's DRI2BufferStencil.

CC: Eric Anholt <eric@anholt.net>
CC: Ian Romanick <idr@freedesktop.org>
CC: Kenneth Graunke <kenneth@whitecape.org>
CC: Kristian Høgsberg <krh@bitplanet.net
Signed-off-by: Chad Versace <chad@chad-versace.us>

src/intel_dri.c

@@ -338,10 +338,20 @@ I830DRI2CreateBuffer(DrawablePtr drawable, unsigned int attachment,
 					hint |= INTEL_CREATE_PIXMAP_TILING_Y;
 					break;
 				}
-			default:
+			case DRI2BufferAccum:
+			case DRI2BufferBackLeft:
+			case DRI2BufferBackRight:
+			case DRI2BufferFakeFrontLeft:
+			case DRI2BufferFakeFrontRight:
+			case DRI2BufferFrontLeft:
+			case DRI2BufferFrontRight:
 				hint |= INTEL_CREATE_PIXMAP_TILING_X;
 				break;
-			}
+			default:
+				free(privates);
+				free(buffer);
+				return NULL;
+                        }
 		}
 
 		pixmap = screen->CreatePixmap(screen,