Avoid calling memchr with a zero range as this is undefined behavior.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 518e96a99bfc0c1cf6f636793a5784d5e0373a5a..f6abd93b605df5a2194278d3ed61dafa229af293 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -3603,7 +3603,7 @@ void FindAsciiStringIndices(Vector<const uint8_t> subject,
   const uint8_t* subject_start = subject.start();
   const uint8_t* subject_end = subject_start + subject.length();
   const uint8_t* pos = subject_start;
-  while (limit > 0) {
+  while ((limit > 0) && (subject_end > pos)) {
     pos = reinterpret_cast<const uint8_t*>(
         memchr(pos, pattern, subject_end - pos));
     if (pos == NULL) return;