RFR: [8056310] Cleanup in WinNTFileSystem_md.c

[Ivan Gerasimov]

Hello!

This is a proposal to make some minor cleanup in WinNTFileSystem_md.c:
- fix a typo in error message,
- use wide char constant for consistency,
- avoid an array reallocation for power-of-two sizes,
- avoid a very unlikely memory leak (when frompath != NULL && topath == 
NULL).

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8056310
WEBREV: http://cr.openjdk.java.net/~igerasim/8056310/0/webrev/

Sincerely yours,
Ivan