st/mesa: Don't access members of NULL pointers

Should be harmless, but UBSAN complains about it and fills the logs with
noise.

../src/mesa/state_tracker/st_manager.c:523:27: runtime error: member access within null pointer of type 'struct st_framebuffer'"}
    #0 0xaad4e89c in st_framebuffer_reference ../src/mesa/state_tracker/st_manager.c:523"}
    #1 0xaad4e89c in st_api_make_current ../src/mesa/state_tracker/st_manager.c:1091"}
    #2 0xaab69e0e in dri_make_current ../src/gallium/state_trackers/dri/dri_context.c:301"}
    #3 0xaab48fd2 in driBindContext ../src/mesa/drivers/dri/common/dri_util.c:581"}
    #4 0xb682a122 in dri2_make_current ../src/egl/drivers/dri2/egl_dri2.c:1625"}
    #5 0xb67f95a4 in eglMakeCurrent ../src/egl/main/eglapi.c:884"}
    #6 0x4c2b0e in tcu::surfaceless::EglRenderContext::EglRenderContext(glu::RenderConfig const&, tcu::CommandLine const&) (/deqp/modules/gles2/deqp-gles2+0x29b0e)"}
    #7 0x4c3302 in tcu::surfaceless::ContextFactory::createContext(glu::RenderConfig const&, tcu::CommandLine const&, glu::RenderContext const*) const (/deqp/modules/gles2/deqp-gles2+0x2a302)"}
    #8 0x73a9b0 in glu::createRenderContext(tcu::Platform&, tcu::CommandLine const&, glu::RenderConfig const&, glu::RenderContext const*) (/deqp/modules/gles2/deqp-gles2+0x2a19b0)"}
    #9 0x73ad86 in glu::createDefaultRenderContext(tcu::Platform&, tcu::CommandLine const&, glu::ApiType) (/deqp/modules/gles2/deqp-gles2+0x2a1d86)"}
    #10 0x4c6a78 in deqp::gles2::Context::Context(tcu::TestContext&) (/deqp/modules/gles2/deqp-gles2+0x2da78)"}
    #11 0x4c3ba0 in deqp::gles2::TestPackage::init() (/deqp/modules/gles2/deqp-gles2+0x2aba0)"}
    #12 0x852fd8 in tcu::TestHierarchyIterator::next() (/deqp/modules/gles2/deqp-gles2+0x3b9fd8)"}
    #13 0x829660 in tcu::TestSessionExecutor::iterate() (/deqp/modules/gles2/deqp-gles2+0x390660)"}
    #14 0x810aac in tcu::App::iterate() (/deqp/modules/gles2/deqp-gles2+0x377aac)"}
    #15 0x4c1d4c in main (/deqp/modules/gles2/deqp-gles2+0x28d4c)"}
    #16 0xb64b6aa8 in __libc_start_main (/lib/arm-linux-gnueabihf/libc.so.6+0x1aaa8)"}

../src/mesa/state_tracker/st_atom.c:115:8: runtime error: member access within null pointer of type 'struct st_program'"}
    #0 0xaae11a58 in check_program_state ../src/mesa/state_tracker/st_atom.c:115"}
    #1 0xaae128f6 in st_validate_state ../src/mesa/state_tracker/st_atom.c:192"}
    #2 0xaadc58c2 in prepare_draw ../src/mesa/state_tracker/st_draw.c:132"}
    #3 0xaadc58c2 in st_draw_vbo ../src/mesa/state_tracker/st_draw.c:184"}
    #4 0xabc4f924 in _mesa_validated_drawrangeelements ../src/mesa/main/draw.c:816"}
    #5 0xabc50240 in _mesa_DrawElements ../src/mesa/main/draw.c:970"}
    #6 0x73ebd2 in glu::CallLogWrapper::glDrawElements(unsigned int, int, unsigned int, void const*) (/deqp/modules/gles2/deqp-gles2+0x2d4bd2)"}
    #7 0x6d86b2 in deqp::gls::FragOpInteractionCase::iterate() (/deqp/modules/gles2/deqp-gles2+0x26e6b2)"}
    #8 0x494d16 in deqp::gles2::TestCaseWrapper::iterate(tcu::TestCase*) (/deqp/modules/gles2/deqp-gles2+0x2ad16)"}
    #9 0x7f9cf2 in tcu::TestSessionExecutor::iterateTestCase(tcu::TestCase*) (/deqp/modules/gles2/deqp-gles2+0x38fcf2)"}
    #10 0x7fa5f0 in tcu::TestSessionExecutor::iterate() (/deqp/modules/gles2/deqp-gles2+0x3905f0)"}
    #11 0x7e1aac in tcu::App::iterate() (/deqp/modules/gles2/deqp-gles2+0x377aac)"}
    #12 0x492d4c in main (/deqp/modules/gles2/deqp-gles2+0x28d4c)"}
    #13 0xb64b9aa8 in __libc_start_main (/lib/arm-linux-gnueabihf/libc.so.6+0x1aaa8)"}

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>

src/mesa/state_tracker/st_atom.c

@@ -84,7 +84,7 @@ static void check_program_state( struct st_context *st )
    /* Flag states used by both new and old shaders to unbind shader resources
     * properly when transitioning to shaders that don't use them.
     */
-   if (unlikely(new_vp != &old_vp->Base)) {
+   if (unlikely(new_vp != (old_vp ? &old_vp->Base : NULL))) {
       if (old_vp)
          dirty |= old_vp->affected_states;
       if (new_vp)

src/mesa/state_tracker/st_manager.c

@@ -520,7 +520,7 @@ void
 st_framebuffer_reference(struct st_framebuffer **ptr,
                          struct st_framebuffer *stfb)
 {
-   struct gl_framebuffer *fb = &stfb->Base;
+   struct gl_framebuffer *fb = stfb ? &stfb->Base : NULL;
    _mesa_reference_framebuffer((struct gl_framebuffer **) ptr, fb);
 }