fix segfault when running glxinfo

src/mesa/drivers/dri/r600/r600_context.c

@@ -453,8 +453,9 @@ void
 r600DestroyContext (__DRIcontextPrivate * driContextPriv)
 {
     GET_CURRENT_CONTEXT (ctx);
-    context_t *context = R700_CONTEXT(ctx);
+    context_t *context = ctx ? R700_CONTEXT(ctx) : NULL;
 
+    if (context)
 	    (context->chipobj.DestroyChipObj)(context->chipobj.pvChipObj);
 }
 

src/mesa/drivers/dri/r600/r600_emit.c

@@ -234,8 +234,10 @@ GLboolean r600DeleteShader(GLcontext * ctx,
 {
     struct radeon_bo * pbo = (struct radeon_bo *)shaderbo;
 
+    if (pbo) {
 	    radeon_bo_unmap(pbo);
 	    radeon_bo_unref(pbo); /* when bo->cref <= 0, bo will be bo_free */
+    }
 
     return GL_TRUE;
 }

src/mesa/drivers/dri/radeon/radeon_common_context.c

@@ -267,6 +267,9 @@ void radeonDestroyContext(__DRIcontextPrivate *driContextPriv )
 		
 		rcommonDestroyCmdBuf(radeon);
 
+#if RADEON_COMMON && defined(RADEON_COMMON_FOR_R600) /* +r6/r7 */
+	    if (!IS_R600_CLASS(screen))
+#endif
 		radeon_destroy_atom_list(radeon);
 
 		if (radeon->state.scissor.pClipRects) {