Fix use of pem_read_buffer() in PK, DHM and X509
diff --git a/include/mbedtls/pem.h b/include/mbedtls/pem.h
index ef94529..f826abd 100644
--- a/include/mbedtls/pem.h
+++ b/include/mbedtls/pem.h
@@ -73,7 +73,7 @@
* \param ctx context to use
* \param header header string to seek and expect
* \param footer footer string to seek and expect
- * \param data source data to look in
+ * \param data source data to look in (must be nul-terminated)
* \param pwd password for decryption (can be NULL)
* \param pwdlen length of password
* \param use_len destination for total length used (set after header is