separate out checks for non-existent file and non-existent dir

Author: zm711

neo/io/__init__.py

@@ -452,12 +452,22 @@ def list_candidate_ios(file_or_folder, ignore_patterns=['*.ini', 'README.txt', '
     # to select all files sharing the `session1-` prefix
     elif file_or_folder.parent.exists():
         filenames = list(file_or_folder.parent.glob(file_or_folder.name + '*'))
+        # if filenames empty and suffix is provided then non-existent file
+        # may be written in current dir. So run check for io
         if len(filenames)==0 and file_or_folder.suffix:
             suffix = file_or_folder.suffix[1:].lower()
             if suffix not in io_by_extension:
                 raise ValueError(f'{suffix} is not a supported format of any IO.')
             return io_by_extension[suffix]
 
+    # If non-existent file in non-existent dir is given check if this 
+    # structure could be created with an io writing the file
+    elif file_or_folder.suffix:
+        suffix = file_or_folder.suffix[1:].lower()
+        if suffix not in io_by_extension:
+            raise ValueError(f'{suffix} is not a supported format of any IO.')
+        return io_by_extension[suffix]
+    
     else:
         raise ValueError(f'{file_or_folder} does not contain data files of a supported format')