message: Repair WebGL, which does not support MapBufferRange.
diff: // change to true to display all GL extensions in the console on start-up
  #define DEBUG_PRINT_EXTENSIONS false
  +#if defined(__EMSCRIPTEN__)
  +#define HAS_MAPBUFFERS 0
  +#else
  +#define HAS_MAPBUFFERS 1
  +#endif
  #define DEBUG_MARKER_NONE 0
  #define DEBUG_MARKER_OPENGL 1
  @@ -1612,7 +1617,7 @@ void OpenGLDriver::updateBuffer(GLenum target,
  assert(buffer->id);
  bindBuffer(target, buffer->id);
  - if (buffer->usage == driver::BufferUsage::STREAM) {
  + if (buffer->usage == driver::BufferUsage::STREAM && HAS_MAPBUFFERS) {
  uint32_t offset = buffer->base + buffer->size;
  offset = (offset + (alignment - 1u)) & ~(alignment - 1u);
  