Fix incorrect check for empty wide string (#1064)

Fixes #1056 

The commit
1d1b3d4
refactored the function to use wide strings, but didn't touch this
check. Because an empty wide string would now be size 2 and not 1, the
empty string would go on and cause the DNS domain list to be replaced
with nothing.

Signed-off-by: @dankmeme01

Author: dankmeme01

src/lib/ares_sysconfig_win.c

@@ -106,7 +106,7 @@ static ares_bool_t get_REG_SZ(HKEY hKey, const WCHAR *leafKeyName, char **outptr
 
   /* Get the value for real */
   res = RegQueryValueExW(hKey, leafKeyName, 0, NULL, (BYTE *)val, &size);
-  if (res != ERROR_SUCCESS || size == 1) {
+  if (res != ERROR_SUCCESS || size == sizeof(WCHAR)) {
     ares_free(val);
     return ARES_FALSE;
   }