Solver::Options::min_relative_decrease can be zero.

Change-Id: I82ae5227ad0f8f6ff21e859e11f0d18ac7d9828c

internal/ceres/solver.cc

diff --git a/internal/ceres/solver.cc b/internal/ceres/solver.cc
index dcdb129..eb578ad 100644
--- a/internal/ceres/solver.cc
+++ b/internal/ceres/solver.cc
@@ -109,7 +109,7 @@
   OPTION_LE_OPTION(min_trust_region_radius, max_trust_region_radius);
   OPTION_LE_OPTION(min_trust_region_radius, initial_trust_region_radius);
   OPTION_LE_OPTION(initial_trust_region_radius, max_trust_region_radius);
-  OPTION_GT(min_relative_decrease, 0.0);
+  OPTION_GE(min_relative_decrease, 0.0);
   OPTION_GE(min_lm_diagonal, 0.0);
   OPTION_GE(max_lm_diagonal, 0.0);
   OPTION_LE_OPTION(min_lm_diagonal, max_lm_diagonal);