Use conservative code to read application setting files

A user who put an executable application or application package into
the directory reserved for GMenu2X's application settings could find
that GMenu2X started 5 or more seconds slower.

LinkApp formerly tried to fully read those binary files as "lines",
which, owing to the fact that binary files might not ever have '\n'
in them, was less than optimal.

A brand new parser stops reading application setting files when it
becomes obvious that nothing good can ever come from reading them.

Thanks to:
* Minseong Joo (주민성), on YouTube, who first proved this bug existed;
* 'kagemusha', on FreeNode, who provided more details as to the cause
  of the bug.