Fixed memory leak in RPC parsing code.

Fixed memory leak in RPC parsing code.
Problem in prs_set_buffer_size() was Realloc returns a NULL when newsize is zero (equivalent to a free()). We were returning a failure here without resetting the buffer_size or the data_p pointer in the prs_struct. And we weren't checking for a failure from prs_set_buffer_size(). So realloc's to zero size were not reflected in the prs_struct: memory leak.
(This used to be commit 590d9ece8449b1feecfe1aa13e61bcd8fea4e5bf)