msvcrt: Add support for multibyte characters in _Strftime.

dlls/msvcrt/tests/time.c

@@ -746,6 +746,16 @@ static void test_strftime(void)
         ok(retA == 17, "expected 17, got %ld\n", retA);
         ok(!strcmp(bufA, "02/30/70 00:00:00"), "got %s\n", bufA);
     }
+
+    if(!setlocale(LC_ALL, "Japanese_Japan.932")) {
+        win_skip("Japanese_Japan.932 locale not available\n");
+        return;
+    }
+
+    /* test with multibyte character */
+    retA = strftime(bufA, 256, "\x82%c", gmt_tm);
+    ok(retA == 3, "expected 3, got %ld\n", retA);
+    ok(!strcmp(bufA, "\x82%c"), "got %s\n", bufA);
 }
 
 static void test_asctime(void)

dlls/msvcrt/time.c

@@ -1078,6 +1078,11 @@ MSVCRT_size_t CDECL _Strftime(char *str, MSVCRT_size_t max, const char *format,
 
     for(ret=0; *format && ret<max; format++) {
         if(*format != '%') {
+            if(MSVCRT_isleadbyte((unsigned char)*format)) {
+                str[ret++] = *(format++);
+                if(ret == max) continue;
+                if(!str[ret]) goto einval_error;
+            }
             str[ret++] = *format;
             continue;
         }