Fix bug that affects reproducibility (#9176)

I made a mistake when I implemented this workaround:


6e299b2e23/projects/ruby/fuzz_ruby_gems.c (L288-L291)

To ensure that the workaround code won't get dead-code-eliminated by a
clever compiler optimization, I decided to feed bytes from the test data
in as an argument:


6e299b2e23/projects/ruby/fuzz_ruby_gems.c (L404-L406)

But that code only gets run on the first iteration (it's protected by a
static variable). That means that the code behaves differently when
you're trying to reproduce a testcase. This PR fixes the bug by
rewinding the bytestream back to the beginning after it's been used for
the workaround code.

projects/ruby/fuzz_ruby_gems.c

@@ -404,6 +404,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     uint32_t x = 0;
     BytesStream_get_uint32_t(&bs, &x);
     workaround_UBSAN_CALLS_THRESHOLD_FOR_UBSAN_BUILD(x);
+
+    // Reset the byte stream
+    ByteStream_init(&bs, data, size);
   }
 
   // Choose a function from `target_functions`.