Fix a incorrect check in reorder_program.cc

Thanks to William Gandler for pointing this out.

Change-Id: I7a4e0eebd2e557f7572df7455d7fa77527c087b6

internal/ceres/reorder_program.cc

diff --git a/internal/ceres/reorder_program.cc b/internal/ceres/reorder_program.cc
index 5d80236..eefb085 100644
--- a/internal/ceres/reorder_program.cc
+++ b/internal/ceres/reorder_program.cc
@@ -279,7 +279,7 @@
 
   CHECK(find(residual_blocks_per_e_block.begin(),
              residual_blocks_per_e_block.end() - 1,
-             0) != residual_blocks_per_e_block.end())
+             0) == residual_blocks_per_e_block.end() - 1)
       << "Congratulations, you found a Ceres bug! Please report this error "
       << "to the developers.";