qga-win: network-get-interfaces command name field bug fix

Network interface name is fetched as an encoded WCHAR array, (wide
character), then it is decoded using the guest's CP_ACP Windows code
page, which is the default code page as configure in the guest's
Windows, then it is returned as a byte array, (char array).

As stated in the BZ#1733165, when renaming a network interface to a
Chinese name and invoking this command, the returned name field has
the (\ufffd) value for each Chinese character the name had, this
value is an indication that the code page does not have the decoding
information for the given character.

This bug is a result of using the CP_ACP code page for decoding which
is an interchangeable code page, instead CP_UTF8 code page should be
used for decoding the network interface's name.

https://bugzilla.redhat.com/show_bug.cgi?id=1733165

Signed-off-by: Bishara AbuHattoum <bishara@daynix.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-win32.c

@@ -1387,12 +1387,12 @@ static IP_ADAPTER_ADDRESSES *guest_get_adapters_addresses(Error **errp)
 static char *guest_wctomb_dup(WCHAR *wstr)
 {
     char *str;
-    size_t i;
+    size_t str_size;
 
-    i = wcslen(wstr) + 1;
-    str = g_malloc(i);
-    WideCharToMultiByte(CP_ACP, WC_COMPOSITECHECK,
-                        wstr, -1, str, i, NULL, NULL);
+    str_size = WideCharToMultiByte(CP_UTF8, 0, wstr, -1, NULL, 0, NULL, NULL);
+    /* add 1 to str_size for NULL terminator */
+    str = g_malloc(str_size + 1);
+    WideCharToMultiByte(CP_UTF8, 0, wstr, -1, str, str_size, NULL, NULL);
     return str;
 }