Fix typo in cmake find netCDF causing failure on blank responses

[islas]

TYPE: bug fix

KEYWORDS: netcdf, cmake

SOURCE: internal

DESCRIPTION OF CHANGES:
Problem:
Certain versions of netCDF with particular configurations return a blank when queried with nc-config. To prevent a null argument expansion in CMake we should check for variable emptiness and if empty assume the queried feature is not present. There is a typo copied from the FindnetCDF-Fortran.cmake module causing this check to never get exercised leading to failed configuration due to syntax errors.

Solution:
Correct the typo to reference the netCDF variables rather than the netCDF-Fortran ones.

TESTS CONDUCTED:

1. Tested against netCDF 4.7.2 without szlib (--has-szlib -> )

RELEASE NOTE: Bug fix in CMake FindnetCDF.cmake for empty --has-* nc-config fields

[weiwangncar]

The regression test results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None