cmd: Reset totals after trailer output.

Otherwise, sums are inherited between drives.
For instance, dir /s z:\tmp c:\windows\system32\drivers\etc shows
an incorrect summary for drive c.

programs/cmd/directory.c

@@ -937,6 +937,7 @@ void WCMD_directory (WCHAR *args)
       if (lastDrive != '?') {
         trailerReqd = FALSE;
         WCMD_dir_trailer(prevEntry->dirName);
+        byte_total = file_total = dir_total = 0;
       }
 
       lastDrive = towupper(thisEntry->dirName[0]);