[trivialre] fix past-end-of-string access in MatchSubstring

Thanks goes to MSVC's string_view asserts that check this.

benchmark/trivialre.h

@@ -58,14 +58,14 @@ inline bool MatchSubstring(const Matcher& m, std::string_view str) {
   size_t sz = str.size();
   CB succeed = [](std::string_view str, bool line_start) { return true; };
   bool line_start = true;
-  for (size_t i = 0; i <= sz; i++) {
+  for (size_t i = 0; i < sz; i++) {
     if (m(str, line_start, succeed)) {
       return true;
     }
     line_start = (str[0] == '\n');
     str.remove_prefix(1);
   }
-  return false;
+  return m("", line_start, succeed);
 }
 
 Matcher CompileREOrDie(std::string_view str);

benchmark/trivialre_test.cc

@@ -154,6 +154,8 @@ TEST(TrivialRETest, Runnings) {
       {"^a", "+a", "-ba", "+b\na"},
       {"a$", "+a\nb", "+ba", "+b\na"},
       {"a$\\nb", "+a\nb"},
+      {"$", "+", "+aaa"},
+      {"^$", "+", "-aaa", "+aaa\n"},
   };
 
   for (const auto& vec : cases2) {