Adding edge case fix

[germa89]

I had a report where using:

nx = np.array(1)
mapdl.nsel("s","loc","x", nx)

will trigger the following error:

TypeError: len() of unsized object

And it due to the fact that numpy arrays made of single scalar don't support len() function.
This is a veeeery weird edge case, but yeah. Let's fix it.

[codecov]

Codecov Report

Merging #1520 (070a1ef) into main (157f0bf) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1520   +/-   ##
=======================================
  Coverage   81.76%   81.76%           
=======================================
  Files          43       43           
  Lines        6784     6784           
=======================================
  Hits         5547     5547           
  Misses       1237     1237           

[germa89]

I still need to double check with Ansys lab team

[germa89]

LGTM.