patch 8.0.0888: compiler warnings with 64 bit build

Problem:    Compiler warnings with 64 bit build.
Solution:   Add type cast of change the type. (Mike Williams)
diff --git a/src/message.c b/src/message.c
index e548fc0..62e6bfe 100644
--- a/src/message.c
+++ b/src/message.c
@@ -2639,7 +2639,7 @@
 # if defined(FEAT_MBYTE) && !defined(FEAT_GUI_MSWIN)
     if (enc_codepage >= 0 && (int)GetConsoleCP() != enc_codepage)
     {
-	int	inlen = STRLEN(str);
+	int	inlen = (int)STRLEN(str);
 	int	outlen;
 	WCHAR	*widestr = (WCHAR *)enc_to_utf16(str, &inlen);