Returns the value associated with key under group_name as a signed 64-bit integer.
This is similar to get_integer but can return 64-bit results without truncation.
| this |
a non-null KeyFile |
| group_name |
a non-null group name |
| key |
a non-null key |
|
the value associated with the key as a signed 64-bit integer, or 0 if the key was not found or could not be parsed. |