Fix MSVC6 warnings. (spotted by Tim Peters)
diff --git a/Modules/cjkcodecs/_big5.c b/Modules/cjkcodecs/_big5.c
index 8f9a290..2ba0bc5 100644
--- a/Modules/cjkcodecs/_big5.c
+++ b/Modules/cjkcodecs/_big5.c
@@ -18,7 +18,7 @@
 
         if (c < 0x80) {
             RESERVE_OUTBUF(1)
-            **outbuf = c;
+            **outbuf = (unsigned char)c;
             NEXT(1, 1)
             continue;
         }