doc: clarify napi_get_value_string_* for bufsize 0

PR-URL: #58158
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>

Author: tniessen

doc/api/n-api.md

@@ -3689,6 +3689,8 @@ napi_status napi_get_value_string_latin1(napi_env env,
   is returned in `result`.
 * `[in] bufsize`: Size of the destination buffer. When this value is
   insufficient, the returned string is truncated and null-terminated.
+  If this value is zero, then the string is not returned and no changes are done
+  to the buffer.
 * `[out] result`: Number of bytes copied into the buffer, excluding the null
   terminator.
 
@@ -3720,6 +3722,8 @@ napi_status napi_get_value_string_utf8(napi_env env,
   returned in `result`.
 * `[in] bufsize`: Size of the destination buffer. When this value is
   insufficient, the returned string is truncated and null-terminated.
+  If this value is zero, then the string is not returned and no changes are done
+  to the buffer.
 * `[out] result`: Number of bytes copied into the buffer, excluding the null
   terminator.
 
@@ -3750,6 +3754,8 @@ napi_status napi_get_value_string_utf16(napi_env env,
   null terminator is returned.
 * `[in] bufsize`: Size of the destination buffer. When this value is
   insufficient, the returned string is truncated and null-terminated.
+  If this value is zero, then the string is not returned and no changes are done
+  to the buffer.
 * `[out] result`: Number of 2-byte code units copied into the buffer, excluding
   the null terminator.