tinydisplay: Set correct number of depth bits in buffer

panda/src/tinydisplay/tinyGraphicsBuffer.cxx

@@ -136,6 +136,8 @@ open_buffer() {
     return false;
   }
 
+  _fb_properties.set_depth_bits(ZB_Z_BITS);
+
   tinygsg->_current_frame_buffer = _frame_buffer;
 
   tinygsg->reset_if_new();