Fixed MaterialEditTextPreference crash when opened more than once. Resolved #330.

library/src/main/java/com/afollestad/materialdialogs/prefs/MaterialEditTextPreference.java

@@ -77,6 +77,8 @@ public class MaterialEditTextPreference extends DialogPreference {
         // Create our layout, put the EditText inside, then add to dialog
         ViewGroup layout = (ViewGroup) LayoutInflater.from(context).inflate(R.layout.md_input_dialog_stub, null);
         mEditText.append(mValue);
+        if (mEditText.getParent() != null)
+            ((ViewGroup) mEditText.getParent()).removeView(mEditText);
         layout.addView(mEditText, new LinearLayout.LayoutParams(
                 ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT));