Update `array_sum` example

examples/array_sum/main.c

@@ -37,9 +37,13 @@ int main(int argc, char * argv[])
         fmpi_data_out(ctx, &out),
         fmpi_data_1d_in(ctx, in, in_size)
     );
-    fmpi_run_task(ctx, &array_sum_task);
+    if(fmpi_run_task(ctx, &array_sum_task) != FMPI_SUCCESS) {
+        printf("Error rank=%d: fmpi_run_task()\n", fmpi_world_rank(ctx));
+    }
     printf("rank=%d local sum=%ld\n", fmpi_world_rank(ctx), out);
-    fmpi_task_finalize(ctx, &array_sum_task, FMPI_TASK_OP_SUM);
+    if(fmpi_task_finalize(ctx, &array_sum_task, FMPI_TASK_OP_SUM) != FMPI_SUCCESS) {
+        printf("Error rank=%d: fmpi_task_finalize()\n", fmpi_world_rank(ctx));
+    }
     fmpi_root_printf(ctx, "global sum=%ld\n", out);
     fmpi_exit(&ctx);
     return EXIT_SUCCESS;