usp10: Mark a fall-through in a switch statement

[Andrew Talbot]

Changelog:
    usp10: Mark a fall-through in a switch statement.

diff --git a/dlls/usp10/bidi.c b/dlls/usp10/bidi.c
index 9c3942c..6539201 100644
--- a/dlls/usp10/bidi.c
+++ b/dlls/usp10/bidi.c
@@ -770,6 +770,7 @@ BOOL BIDI_DetermineLevels(
             case S:
             case WS:
             case ON: chartype[j] = N;
+                /* fall through */
             default: continue;
         }