Make the fuzzer check size before computing rsize.
Make the fuzzer check size before computing rsize.

Likewise for fanout and rfanout.

Change-Id: I5182fb69bf9c391cce7857519d91b1d00a501f42
Reviewed-on: https://code-review.googlesource.com/c/34010
Reviewed-by: Paul Wankadia <62d4e38bb1380f055ec4b899baa75e52af09c5f7@google.com>

google/re2,google/re2,google/re2,google/re2,google/re2