Fix RealDataBench subspan and version API contract violations

- Use subspan count `line.size() - 2` instead of `line.size()` to avoid reading past the line bounds, and guard lines shorter than the two-byte prefix.
- Clamp `readVersion` and `setOldestVersion` arguments to `0` so the conflict set never receives negative, non-monotonic versions during the warmup phase.

Fixes #58.

RealDataBench.cpp

@@ -1,5 +1,6 @@
 #include <ConflictSet.h>
 
+#include <algorithm>
 #include <cerrno>
 #include <chrono>
 #include <cstdio>
@@ -77,10 +78,10 @@ int main(int argc, const char **argv) {
       begin = end + 1;
       end = (uint8_t *)memchr(begin, '\n', size);
 
-      if (line.size() > 0 && line[0] == 'P') {
-        write = line.subspan(2, line.size());
-      } else if (line.size() > 0 && line[0] == 'L') {
-        reads.push_back(line.subspan(2, line.size()));
+      if (line.size() >= 2 && line[0] == 'P') {
+        write = line.subspan(2, line.size() - 2);
+      } else if (line.size() >= 2 && line[0] == 'L') {
+        reads.push_back(line.subspan(2, line.size() - 2));
       } else if (line.empty()) {
         {
           readRanges.resize(reads.size());
@@ -90,7 +91,7 @@ int main(int argc, const char **argv) {
             iter->begin.len = read.size();
             checkBytes += read.size();
             iter->end.len = 0;
-            iter->readVersion = version - 100;
+            iter->readVersion = std::max<int64_t>(0, version - 100);
             ++iter;
           }
         }
@@ -121,7 +122,7 @@ int main(int argc, const char **argv) {
         }
 
         timer = now();
-        cs.setOldestVersion(version - 10000);
+        cs.setOldestVersion(std::max<int64_t>(0, version - 10000));
         gcTime += now() - timer;
       }
     }