riemann: A zero floating point value is ok

When strtof() returns zero, that's ok, use it.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
basicfuncs-plus: New module

This new module adds a $(//) template function to do floating-point
division.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>