[ModelicaSystem] update convertMo2Fmu() and convertFmu2Mo() to use pathlib.Path()

Author: syntron

OMPython/ModelicaSystem.py

@@ -1640,7 +1640,7 @@ def convertFmu2Mo(
             raise ModelicaSystemError(f"Missing FMU file: {fmu_path.as_posix()}")
 
         filename = self._requestApi(apiName='importFMU', entity=fmu_path.as_posix())
-        filepath = self._work_dir / filename
+        filepath = self._getconn.omcpath(filename)
 
         # report proper error message
         if not filepath.is_file():