Fix size computation in replace_repeat() for special_case REPEAT_WITH_Q.

Fix size computation in replace_repeat() for special_case REPEAT_WITH_Q.
This resulted in the NUL terminator being written to the end of the
buffer which was not the same as the end of the string.  That in
turn caused garbage bytes from malloc() to be processed.  Also
change the NUL termination to be less error prone by writing the
NUL immediately after the last byte copied.  OK sthen@