In microdesc_cache_reload(), set journal length to length of string we read

Hopefully this will fix CID 1444769.

src/feature/nodelist/microdesc.c

@@ -536,8 +536,8 @@ microdesc_cache_reload(microdesc_cache_t *cache)
   journal_content = read_file_to_str(cache->journal_fname,
                                      RFTS_IGNORE_MISSING, &st);
   if (journal_content) {
-    cache->journal_len = (size_t) st.st_size;
-    warn_if_nul_found(journal_content, cache->journal_len, 0,
+    cache->journal_len = strlen(journal_content);
+    warn_if_nul_found(journal_content, (size_t)st.st_size, 0,
                       "reading microdesc journal");
     added = microdescs_add_to_cache(cache, journal_content,
                                     journal_content+st.st_size,