fix hybrid uninitialized warning

[jmackay2]

There is an error when building on Ubuntu 24.04:

gtsam/examples/Hybrid_City10000.cpp:207:16: error: ‘key_t’ may be used uninitialized [-Werror=maybe-uninitialized]
  207 |   write_results(results, (key_t + 1), "HybridISAM_city10000.txt");

This solves the error by initializing key_t to remove the warning. This was tested by performing a successful build.

[varunagrawal]

So strange, I don't get this issue? What version of GCC are you using? It would behoove us to add a CI check with that version if it is stricter.

[varunagrawal]

Thank you!

[jmackay2]

So strange, I don't get this issue? What version of GCC are you using? It would behoove us to add a CI check with that version if it is stricter.

I'm on Ubuntu 24.04 with gcc 13.3.0.