MDEV-8162 func_str crashes on SELECT AES_DECRYPT(AES_ENCRYPT(...)) on line 107

encrypting 0 byte string *is* possible

mysys_ssl/my_crypt.cc

@@ -71,8 +71,6 @@ static int block_crypt(CipherMode cipher, Dir dir,
 {
   int tail= source_length % MY_AES_BLOCK_SIZE;
 
-  DBUG_ASSERT(source_length);
-
   if (likely(source_length >= MY_AES_BLOCK_SIZE || !no_padding))
   {
 #ifdef HAVE_YASSL
@@ -139,7 +137,9 @@ static int block_crypt(CipherMode cipher, Dir dir,
 #endif
   }
 
-  if (no_padding && tail)
+  if (no_padding)
+  {
+    if (tail)
     {
       /*
         Not much we can do, block ciphers cannot encrypt data that aren't
@@ -161,6 +161,7 @@ static int block_crypt(CipherMode cipher, Dir dir,
       const uchar *m= mask;
       while (s < e)
         *d++ = *s++ ^ *m++;
+    }
     *dest_length= source_length;
   }