mesa: simplify _mesa_IsVertexArray()

_mesa_lookup_vao() already returns NULL if id is zero.

v2: - change the conditional (Ian)

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com> (v1)

src/mesa/main/arrayobj.c

@@ -605,14 +605,9 @@ _mesa_IsVertexArray( GLuint id )
    GET_CURRENT_CONTEXT(ctx);
    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, GL_FALSE);
 
-   if (id == 0)
-      return GL_FALSE;
-
    obj = _mesa_lookup_vao(ctx, id);
-   if (obj == NULL)
-      return GL_FALSE;
 
-   return obj->EverBound;
+   return obj != NULL && obj->EverBound;
 }