Add valid handle returned when .pl2 file is opened

Author: cheydrick

neo/rawio/plexon2rawio/plexon2rawio.py

@@ -130,6 +130,11 @@ def __init__(self, filename, pl2_dll_file_path=None):
 
         # Open the file.
         self.pl2reader.pl2_open_file(self.filename)
+        
+        # Verify the file handle is valid.
+        if self.pl2reader._file_handle.value == 0:
+            self.pl2reader._print_error()
+            raise Exception(f"Opening {self.filename} failed.")
 
     def _source_name(self):
         return self.filename