[BUG] FDGA: Crashes when token_map_path file has wrong format

[HugoSoszynski]

Describe the bug
When the file contained in the "token_map_path" field of the config is not properly formatted the filter crashes without logging.

Platform (please complete the following information):

• OS (version): FreeBSD (12.0)
• Darwin version: 1.0

To Reproduce
Steps to reproduce the behavior:

1. Generate a random file
2. Set the field "token_map_path" to ths file
3. Start fdga

Expected behavior
Log a CRITICAL error with the proper message and quit gracefully.

Additional context
Hint: Look around line 140-143 of fdga/Generator.cpp