[piper] format_to_n does not terminate...

src/piper.looper.cc

@@ -52,14 +52,14 @@ write_timestamp(int fd, log_level_t level, off_t woff)
     struct timeval tv;
 
     gettimeofday(&tv, nullptr);
-    fmt::format_to_n(time_str,
-                     sizeof(time_str),
-                     FMT_STRING("{}.{}:{};"),
-                     tv.tv_sec,
-                     tv.tv_usec,
-                     level_names[level][0]);
-
-    return pwrite(fd, time_str, strlen(time_str), woff);
+    auto fmt_res = fmt::format_to_n(time_str,
+                                    sizeof(time_str),
+                                    FMT_STRING("{}.{}:{};"),
+                                    tv.tv_sec,
+                                    tv.tv_usec,
+                                    level_names[level][0]);
+
+    return pwrite(fd, time_str, fmt_res.size, woff);
 }
 
 namespace lnav {