msvcrt: Fix handling of unsigned chars in scanf format.

dlls/msvcrt/scanf.h

@@ -699,7 +699,7 @@ _FUNCTION_ {
 	 * a matching non-white-space character. */
         else {
             /* check for character match */
-            if (nch == *format) {
+            if (nch == (unsigned char)*format) {
 		nch = _GETC_(file);
             } else break;
         }

dlls/msvcrt/tests/scanf.c

@@ -251,6 +251,10 @@ static void test_sscanf( void )
     ok(ret == 2, "got %d\n", ret);
     ok(!strcmp(buffer, "test"), "buf %s\n", buffer);
     ok(!strcmp(buffer1, "value\xda"), "buf %s\n", buffer1);
+
+    ret = sscanf("\x81test", "\x81%s", buffer);
+    ok(ret == 1, "got %d\n", ret);
+    ok(!strcmp(buffer, "test"), "buf = %s\n", buffer);
 }
 
 static void test_sscanf_s(void)