Fix bugs dereferencing NULL pointer if the MATLAB variable is empty with NULL data field and marked as complex
Fix bugs dereferencing NULL pointer if the MATLAB variable is empty with NULL data field and marked as complex

* src/mat5.c (null_complex_data): Added

* src/mat5.c (WriteCellArrayField,WriteCompressedCellArrayField,
  WriteStructField,WriteCompressedStructField,Mat_VarWrite5): If a
      dense numeric array is marked as complex and matvar->data is
      NULL, dereference null_complex_data when getting pointers to
      the real and imaginary parts which are initialized to NULL so
      the required data tag is written

CBL-ORION/matio-sf-mirror,tbeu/matio,telehan/libmatio,NJannasch/matio,MaartenBent/matio,martinichka/matio-coder,CBL-ORION/matio-sf-mirror,CBL-ORION/matio,MaartenBent/matio,tbeu/matio,NJannasch/matio,tbeu/matio,MaartenBent/matio,CBL-ORION/matio,telehan/libmatio,tbeu/matio,MaartenBent/matio,martinichka/matio-coder,martinichka/matio-coder