fuzz: don't run on big haystacks

We keep beating back the OSS-fuzz timeouts. It keeps finding bigger and
bigger haystacks with even smallish regexes that have Unicode word
boundaries in them. This results in using the PikeVM which is just slow.
There's really nothing to be done other than to tell the fuzzer: "this
is OK."

fuzz/fuzz_targets/fuzz_regex_match.rs

@@ -14,6 +14,15 @@ fuzz_target!(|data: &[u8]| {
         let char_index = data.char_indices().nth(split_off_point);
         if let Some((char_index, _)) = char_index {
             let (pattern, input) = data.split_at(char_index);
+            // If the haystack is big, don't use it. The issue is that
+            // the fuzzer is compiled with sanitizer options and it makes
+            // everything pretty slow. This was put in here as a result of
+            // getting timeout errors from OSS-fuzz. There's really nothing to
+            // be done about them. Unicode word boundaries in the PikeVM are
+            // slow. It is what it is.
+            if input.len() >= 8 * (1 << 10) {
+                return;
+            }
             let result =
                 regex::RegexBuilder::new(pattern).size_limit(1 << 18).build();
             if let Ok(re) = result {