Minor fix to reject a line search config with negative L-BFGS rank.

Change-Id: Iad4c678efe574ef6696c34bd2a0ce61a504c7344

internal/ceres/solver_impl.cc

diff --git a/internal/ceres/solver_impl.cc b/internal/ceres/solver_impl.cc
index 8fc1305..d6ef731 100644
--- a/internal/ceres/solver_impl.cc
+++ b/internal/ceres/solver_impl.cc
@@ -647,7 +647,7 @@
     LOG(ERROR) << summary->error;
     return;
   }
-  if (original_options.max_lbfgs_rank == 0) {
+  if (original_options.max_lbfgs_rank <= 0) {
     summary->error =
         string("Invalid configuration: require max_lbfgs_rank > 0");
     LOG(ERROR) << summary->error;