Fix bug with period not separating file extension

bdfr/file_name_formatter.py

@@ -110,8 +110,11 @@ class FileNameFormatter:
         index = f'_{str(index)}' if index else ''
         if not resource.extension:
             raise BulkDownloaderException(f'Resource from {resource.url} has no extension')
-        ending = index + resource.extension
         file_name = str(self._format_name(resource.source_submission, self.file_format_string))
+        if not re.match(r'.*\.$',file_name) and not re.match(r'^\..*',resource.extension):
+            ending = index + '.' + resource.extension
+        else:
+            ending = index + resource.extension
 
         try:
             file_path = self._limit_file_name_length(file_name, ending, subfolder)