scope: Don't use an untrusted string as a printf format

[b4n]

Reported by GCC's -Wformat-security.

[b4n]

Found through nightly builds (http://nightly.geany.org/):

debug.c: In function 'debug_parse':
debug.c:256:4: error: format not a string literal and no format arguments [-Werror=format-security]
    dc_error(error);
    ^

[zhekov]

Thanks. Merged.

[zhekov]

(though the only values of error are currently "binary zero encountered" and "line too long or incomplete")