fix contourf zeros, use pcolor instead
fix contourf zeros, use pcolor instead

fix warning:
```
/usr/lib/python3.8/site-packages/matplotlib/ticker.py:2707: RuntimeWarning: divide by zero encountered in log10
  majorstep_no_exponent = 10 ** (np.log10(majorstep) % 1)
/usr/lib/python3.8/site-packages/matplotlib/ticker.py:2723: RuntimeWarning: invalid value encountered in double_scalars
  tmin = ((vmin - t0) // minorstep + 1) * minorstep
```

shmilee/gdpy3,shmilee/gdpy3,shmilee/gdpy3,shmilee/gdpy3