Fix call to v7.3 function without HDF5
Fix call to v7.3 function without HDF5

* src/mat.c (Mat_VarReadData): Add preprocessor conditional around call to
      Mat_VarReadData73 and return an error code if not compiled with MAT73

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