[win32] fix a weird error in the environment variable code for win32 …

…where we were passing a char* instead of a STRING* like we should ahve been

git-svn-id: https://svn.parrot.org/parrot/trunk@41961 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

config/gen/platform/win32/env.c

@@ -131,7 +131,7 @@ Parrot_unsetenv(PARROT_INTERP, STRING *name)
    string -- in other words, by specifying only varname=.
        -- _putenv, _wputenv (CRT) documentation
 */
-    Parrot_setenv(interp, name, "");
+    Parrot_setenv(interp, name, Parrot_str_new(interp, "", 0));
 }
 
 /*