Fix return value not checked issue reported by Coverity (#1156)

Fix return value not checked issue in function init_wasm_timer,
reported by Coverity

samples/simple/src/iwasm_main.c

@@ -518,9 +518,6 @@ iwasm_main(int argc, char *argv[])
         return -1;
     }
 
-    /* timer manager */
-    init_wasm_timer();
-
     /* connection framework */
     if (!init_connection_framework()) {
         goto fail1;
@@ -531,6 +528,11 @@ iwasm_main(int argc, char *argv[])
         goto fail2;
     }
 
+    /* timer manager */
+    if (!init_wasm_timer()) {
+        goto fail3;
+    }
+
     /* add the sys sensor objects */
     add_sys_sensor("sensor_test1", "This is a sensor for test", 0, 1000,
                    read_test_sensor, config_test_sensor);
@@ -552,6 +554,8 @@ iwasm_main(int argc, char *argv[])
     app_manager_startup(&interface);
 
     exit_wasm_timer();
+
+fail3:
     exit_sensor_framework();
 
 fail2: