linear_solver: don't make samples crash if solver are unavailable

Author: Mizux

ortools/linear_solver/samples/java/IntegerProgramming.java

@@ -24,7 +24,8 @@ public class IntegerProgramming {
   private static void runIntegerProgrammingExample(String solverType) {
     MPSolver solver = MPSolver.createSolver(solverType);
     if (solver == null) {
-      throw new AssertionError("Could not create solver " + solverType);
+      System.out.println("Could not create solver " + solverType);
+      return;
     }
     double infinity = Double.POSITIVE_INFINITY;
     // x1 and x2 are integer non-negative variables.

ortools/linear_solver/samples/java/LinearProgramming.java

@@ -26,7 +26,8 @@ public class LinearProgramming {
   private static void runLinearProgrammingExample(String solverType, boolean printModel) {
     MPSolver solver = MPSolver.createSolver(solverType);
     if (solver == null) {
-      throw new AssertionError("Could not create solver " + solverType);
+      System.out.println("Could not create solver " + solverType);
+      return;
     }
     double infinity = Double.POSITIVE_INFINITY;
     // x1, x2 and x3 are continuous non-negative variables.