Close the bal_problem file when done reading it.

Change-Id: I2755822cd2caf4019059e5b4a50f30077142e37f

examples/bal_problem.cc

diff --git a/examples/bal_problem.cc b/examples/bal_problem.cc
index 2ab35e4..6c65a20 100644
--- a/examples/bal_problem.cc
+++ b/examples/bal_problem.cc
@@ -83,6 +83,8 @@
     FscanfOrDie(fptr, "%lf", parameters_ + i);
   }
 
+  fclose(fptr);
+
   use_quaternions_ = use_quaternions;
   if (use_quaternions) {
     // Switch the angle-axis rotations to quaternions.