For backwards compatibility, bind fake backbuffer FBO instead of 0

* In newer captures we should always serialise an actual correct ID for the
  backbuffer, but in older captures an empty resource ID will be serialised, so
  we should pick this up and bind the backbuffer.

renderdoc/driver/gl/wrappers/gl_framebuffer_funcs.cpp

@@ -1439,6 +1439,8 @@ bool WrappedOpenGL::Serialise_glBindFramebuffer(SerialiserType &ser, GLenum targ
 
   if(IsReplayingAndReading())
   {
+    if(framebuffer.name == 0)
+      framebuffer.name = m_FakeBB_FBO;
     m_Real.glBindFramebuffer(target, framebuffer.name);
   }