'rndc dnstap --roll' fix was incomplete

1178                                        }
    	21. Condition i < versions, taking true branch.
1179                                        if (i < versions) {
    	
CID 305429 (#1 of 1): Out-of-bounds read (OVERRUN)
22. overrun-local: Overrunning array of 2048 bytes at byte offset 2048 by dereferencing pointer &to_keep[i + 1]. [Note: The source code implementation of the function has been overridden by a builtin model.]
1180                                                memmove(&to_keep[i + 1],
1181                                                        &to_keep[i],
1182                                                        sizeof(to_keep[0]) *
1183                                                                (versions - i -
1184                                                                 1));
1185                                                to_keep[i] = version;
1186                                        }
1187                                }
1188                        }