bss_file.c: fix MSC 6.0 warning.

crypto/bio/bss_file.c

diff --git a/crypto/bio/bss_file.c b/crypto/bio/bss_file.c
index cb2abea..ba4f8e9 100644
--- a/crypto/bio/bss_file.c
+++ b/crypto/bio/bss_file.c
@@ -274,7 +274,7 @@
 #endif
 #ifdef UP_fsetmod
 		if (b->flags&BIO_FLAGS_UPLINK)
-			UP_fsetmod(b->ptr,num&BIO_FP_TEXT?'t':'b');
+			UP_fsetmod(b->ptr,(char)((num&BIO_FP_TEXT)?'t':'b'));
 		else
 #endif
 		{