Android: fix crash when opening settings on pre-7 devices

android/src/com/reecedunn/espeak/TtsSettingsActivity.java

     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
 
-        PreferenceManager preferenceManager = getPreferenceManager();
-        preferenceManager.setStorageDeviceProtected ();
-
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N)
+        {
+            PreferenceManager preferenceManager = getPreferenceManager();
+            preferenceManager.setStorageDeviceProtected ();
+        }
         // Migrate old eyes-free settings to the new settings:
 
         storageContext = EspeakApp.getStorageContext();

android/src/com/reecedunn/espeak/preference/SeekBarPreference.java

 import android.content.Context;
 import android.content.DialogInterface;
 import android.content.SharedPreferences;
+import android.os.Bundle;
 import android.preference.DialogPreference;
 import android.preference.PreferenceManager;
 import android.util.AttributeSet;
         String text = Integer.toString(mProgress);
         callChangeListener(text);
         if (shouldCommit()) {
-            PreferenceManager preferenceManager = getPreferenceManager();
-            preferenceManager.setStorageDeviceProtected ();
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N)
+            {
+                PreferenceManager preferenceManager = getPreferenceManager();
+                preferenceManager.setStorageDeviceProtected ();
+            }
             SharedPreferences.Editor editor = getEditor();
             editor.putString(getKey(), text);
             editor.commit();

android/src/com/reecedunn/espeak/preference/SpeakPunctuationPreference.java

 import android.content.Context;
 import android.content.DialogInterface;
 import android.content.SharedPreferences;
+import android.os.Bundle;
 import android.preference.DialogPreference;
 import android.preference.PreferenceManager;
 import android.text.Editable;
                 onDataChanged(level, characters);
 
                 if (shouldCommit()) {
-                    PreferenceManager preferenceManager = getPreferenceManager();
-                    preferenceManager.setStorageDeviceProtected();
+                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N)
+                    {
+                        PreferenceManager preferenceManager = getPreferenceManager();
+                        preferenceManager.setStorageDeviceProtected ();
+                    }
                     SharedPreferences.Editor editor = getEditor();
                     if (editor != null) {
                         editor.putString(VoiceSettings.PREF_PUNCTUATION_CHARACTERS, characters);

android/src/com/reecedunn/espeak/preference/VoiceVariantPreference.java

 import android.content.Context;
 import android.content.DialogInterface;
 import android.content.SharedPreferences;
+import android.os.Bundle;
 import android.preference.DialogPreference;
 import android.preference.PreferenceManager;
 import android.util.AttributeSet;
             case DialogInterface.BUTTON_POSITIVE:
                 onDataChanged();
                 if (shouldCommit()) {
-                    PreferenceManager preferenceManager = getPreferenceManager();
-                    preferenceManager.setStorageDeviceProtected();
+                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N)
+                    {
+                        PreferenceManager preferenceManager = getPreferenceManager();
+                        preferenceManager.setStorageDeviceProtected ();
+                    }
                     SharedPreferences.Editor editor = getEditor();
                     if (editor != null) {
                         VoiceVariant variant = variants[mCategoryIndex][mVariantIndex].getVariant();