Fixed the number of rows set for terrain parameters

[TonyGorgy]

nbRows and nbColumns are assigned in the correct order.
./ legged_robot.py
hf_params.nbRows = self.terrain.tot_cols -> hf_params.nbRows = self.terrain.tot_rows
hf_params.nbColumns = self.terrain.tot_rows -> hf_params.nbColumns = self.terrain.tot_cols

[luoye2333]

@TonyGorgy @nikitardn
I also noticed this bug: when using the height field, the terrain generation is incorrect. Following @TonyGorgy 's method to fix it, although the terrain is correct, the env_origins are transposed, causing incorrect positions when reset_root_state is called.

transpose() should be added when adding the height field, while keeping nbRows and nbColumns unchanged.

self.gym.add_heightfield(self.sim, self.terrain.heightsamples.transpose(), hf_params) # column-major order