Fix 'writing 1 byte into region of size 0'

src/sietch.h

@@ -29,8 +29,8 @@ SendManyRecipient newSietchRecipient(string zaddr) {
     // Sietch zouts have random data in their memos so they are indistinguishable from
     // encrypted data being stored in the memo field
     char hex[] = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};
-    // memo field is 512 bytes or 1024 hex chars
-    char str[1024];
+    // memo field is 512 bytes or 1024 hex chars plus a null byte
+    char str[1025];
     for(int i=0;i<1024;i++) {
       str[i] = hex[GetRandInt(16)];
     }