Preferences examples: add begin return value check

  - This library works only if WiFi firmware version is greater than 0.3.0

Author: pennam

libraries/Preferences/examples/Prefs2Struct/Prefs2Struct.ino

@@ -17,7 +17,11 @@ typedef struct {
 void setup() {
   Serial.begin(115200);
 
-  prefs.begin("schedule"); // use "schedule" namespace
+  if (!prefs.begin("schedule")) { // use "schedule" namespace
+    Serial.println("Cannot initialize preferences");
+    Serial.println("Make sure your WiFi firmware version is greater than 0.3.0");
+    while(1) {};
+  }
   uint8_t content[] = {9, 30, 235, 255, 20, 15, 0, 1}; // two entries
   prefs.putBytes("schedule", content, sizeof(content));
   size_t schLen = prefs.getBytesLength("schedule");

libraries/Preferences/examples/StartCounter/StartCounter.ino

@@ -21,8 +21,11 @@ void setup() {
   // has to use a namespace name to prevent key name collisions. We will open storage in
   // RW-mode (second parameter has to be false).
   // Note: Namespace name is limited to 15 chars.
-  int ret = preferences.begin("my-app", false);
-  Serial.println(ret);
+  if (!preferences.begin("my-app", false)) {
+    Serial.println("Cannot initialize preferences");
+    Serial.println("Make sure your WiFi firmware version is greater than 0.3.0");
+    while(1) {};
+  }
 
   // Remove all preferences under the opened namespace
   //preferences.clear();