Gridspec indexing not matching with multi-legends

[cvanelteren]

Related to #461. When plot multiple legends, rows and cols of loc_axs may result in wrong value here due to hiden panel. I've tried many examples, sometimes legend will be placed in wrong places, and sometimes it will raise errors. e.g:

import ultraplot as pplt
fig,axs=pplt.subplots(ncols=3, nrows=3,refwidth='3cm')
axs.plot([1,2], [1,2], label='line')
fig.legend(ref=axs[0],loc='b') //comment this line, error will go away
fig.legend(ref=axs[:, 1],loc='r')

Originally posted by @gepcel in #459

[gepcel]

All examples I've been testing with works right.

[cvanelteren]

Good @gepcel!