Null check for cipher text to prevent NPE on decryption

Fixes #1703
Closes #1728
// FREEBIE

src/org/thoughtcrime/securesms/database/EncryptingSmsDatabase.java

@@ -24,13 +24,13 @@ import android.util.Pair;
 
 import org.thoughtcrime.securesms.crypto.AsymmetricMasterCipher;
 import org.thoughtcrime.securesms.crypto.AsymmetricMasterSecret;
-import org.whispersystems.textsecure.crypto.InvalidMessageException;
-import org.whispersystems.textsecure.crypto.MasterCipher;
-import org.whispersystems.textsecure.crypto.MasterSecret;
 import org.thoughtcrime.securesms.database.model.DisplayRecord;
 import org.thoughtcrime.securesms.sms.IncomingTextMessage;
 import org.thoughtcrime.securesms.sms.OutgoingTextMessage;
 import org.thoughtcrime.securesms.util.LRUCache;
+import org.whispersystems.textsecure.crypto.InvalidMessageException;
+import org.whispersystems.textsecure.crypto.MasterCipher;
+import org.whispersystems.textsecure.crypto.MasterSecret;
 
 import java.lang.ref.SoftReference;
 import java.util.Collections;
@@ -145,6 +145,10 @@ public class EncryptingSmsDatabase extends SmsDatabase {
       long type         = cursor.getLong(cursor.getColumnIndexOrThrow(SmsDatabase.TYPE));
       String ciphertext = cursor.getString(cursor.getColumnIndexOrThrow(SmsDatabase.BODY));
 
+      if (ciphertext == null) {
+        return new DisplayRecord.Body("", true);
+      }
+
       try {
         if (SmsDatabase.Types.isSymmetricEncryption(type)) {
           String plaintext = plaintextCache.get(ciphertext);