FIX: Remove 0.0 from candidates in solve_discrete_riccati

[oyamad]

The same changes as in the Python side:

1. FIX: Remove 0.0 from candidates in solve_discrete_riccati QuantEcon.py#364
2. FIX: Replace np.isfinite(cn) with cn * EPS < 1 in solve_discrete_riccati QuantEcon.py#361

[codecov-io]

Codecov Report

Merging #185 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #185   +/-   ##
=======================================
  Coverage   90.69%   90.69%           
=======================================
  Files          24       24           
  Lines        1633     1633           
=======================================
  Hits         1481     1481           
  Misses        152      152

Impacted Files	Coverage Δ
src/matrix_eqn.jl	92.53% <100%> (ø)	⬆️

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[sglyon]

Looks good, thank you