glgsg: Fix use after free with gl-force-fbo-color and layered FBO

panda/src/glstuff/glGraphicsBuffer_src.cxx

@@ -419,6 +419,7 @@ rebuild_bitplanes() {
   Texture *attach[RTP_COUNT];
   memset(attach, 0, sizeof(Texture *) * RTP_COUNT);
   _texture_contexts.clear();
+  _textures.clear();
 
   // Sort the textures list into appropriate slots.
   {
@@ -793,6 +794,8 @@ bind_slot(int layer, bool rb_resize, Texture **attach, RenderTexturePlane slot,
       _fb_properties.setup_color_texture(tex);
     }
 
+    _textures.push_back(tex);
+
     TextureContext *tc = tex->prepare_now(glgsg->get_prepared_objects(), glgsg);
     nassertv(tc != nullptr);
     CLP(TextureContext) *gtc = DCAST(CLP(TextureContext), tc);

panda/src/glstuff/glGraphicsBuffer_src.h

@@ -128,6 +128,10 @@ protected:
   typedef pvector<CLP(TextureContext)*> TextureContexts;
   TextureContexts _texture_contexts;
 
+  // List of textures we need to keep a reference to.
+  typedef pvector<PT(Texture)> Textures;
+  Textures _textures;
+
   // The cube map face we are currently drawing to or have just finished
   // drawing to, or -1 if we are not drawing to a cube map.
   int _bound_tex_page;