Check return value of malloc

fixes #27

//FREEBIE

src/Util/Cryptography.m

@@ -112,6 +112,11 @@
     size_t bufferSize = [dataToEncrypt length] + kCCBlockSizeAES128;
     void *buffer      = malloc(bufferSize);
     
+    if (buffer == NULL) {
+        DDLogError(@"Failed to allocate memory.");
+        return nil;
+    }
+
     size_t bytesEncrypted       = 0;
     CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt,
                                           kCCAlgorithmAES128,
@@ -190,6 +195,11 @@
     size_t bufferSize = [dataToDecrypt length] + kCCBlockSizeAES128;
     void *buffer      = malloc(bufferSize);
     
+    if (buffer == NULL) {
+        DDLogError(@"Failed to allocate memory.");
+        return nil;
+    }
+
     size_t bytesDecrypted       = 0;
     CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt,
                                           kCCAlgorithmAES128,