set correct dimension when finding 3- or 4-D array

[PaulWessel]

While we correctly found a higher-dimensioned array than 2, we forgot to update ndims once selecting it.
Closes #6588.

[seisman]

Now it gives me the following errro message. Is it expected?

$ gmt grdinfo -C eraint_uvz.nc
grdinfo [WARNING]: No 3-D array in file eraint_uvz.nc.  Selecting first 3-D slice in the 4-D array z
grdinfo [ERROR]: No 3rd-dimension coordinate vector found in eraint_uvz.nc
grdinfo [ERROR]: gmtapi_import_cube: Unable to examine cube eraint_uvz.nc.
[Session gmt (0)]: Error returned from GMT API: GMT_RUNTIME_ERROR (79)
[Session gmt (0)]: Error returned from GMT API: GMT_RUNTIME_ERROR (79)

[PaulWessel]

Boy, fun with different platforms. I see this:

gmt grdinfo eraint_uvz.nc
grdinfo [WARNING]: No 3-D array in file eraint_uvz.nc. Selecting first 3-D slice in the 4-D array z
eraint_uvz.nc: Title: Geopotential
eraint_uvz.nc: Command:
eraint_uvz.nc: Remark:
eraint_uvz.nc: Gridline node registration used [Geographic grid]
eraint_uvz.nc: Grid file format: ns = GMT netCDF format (16-bit integer), CF-1.7
eraint_uvz.nc: x_min: -180 x_max: 179.25 x_inc: 0.75 (45 min) name: longitude n_columns: 480
eraint_uvz.nc: y_min: -90 y_max: 90 y_inc: 0.75 (45 min) name: latitude n_rows: 241
eraint_uvz.nc: z_min: -180 z_max: -170.25 z_inc: 0.75 name: longitude [degrees_east] n_levels: 14
eraint_uvz.nc: v_min: 66825.5 v_max: 66825.5 name: Geopotential [m2 s-2]
eraint_uvz.nc: scale_factor: -1.7250274675 add_offset: 66825.5 packed z-range: [-0,-0]
eraint_uvz.nc: format: classic
eraint_uvz.nc: Default CPT:

(base) pwessel@MacAttack-> gmt grdinfo eraint_uvz.nc -C
grdinfo [WARNING]: No 3-D array in file eraint_uvz.nc. Selecting first 3-D slice in the 4-D array z
eraint_uvz.nc -180 179.25 -90 90 -180 -170.25 66825.5 66825.5 0.75 0.75 0.75 480 24114 0 1

[PaulWessel]

OK, there was one more place to apply that fix. Try again please.

[seisman]

It works now!