add the annotation in the function of pg_md5_encrypt

src/common/backend/libpq/md5.cpp

@@ -309,6 +309,7 @@ bool pg_md5_encrypt(const char* passwd, const char* salt, size_t salt_len, char*
 {
     size_t passwd_len = strlen(passwd);
     errno_t rc = EOK;
+    /* the length of salt and password is <= SIZE_MAX */
 #ifndef WIN32
     if (unlikely(passwd_len >= SIZE_MAX - salt_len)) {
         return false;
@@ -322,6 +323,7 @@ bool pg_md5_encrypt(const char* passwd, const char* salt, size_t salt_len, char*
     char* crypt_buf = (char*)malloc(passwd_len + salt_len + 1);
     bool ret = false;
 
+    /* the buffer is not exist */
     if (crypt_buf == NULL)
         return false;