win32: Initialize mutexes for static builds for win32

For static win32 builds the mutexes are not initialized (for dynamic
builds it's done when the DLL is loaded). Therefore, add initialization
to the create surface calls.

Cc: Uli Schlachter <psychon@znc.in>
Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>

src/win32/cairo-win32-device.c

@@ -131,6 +131,8 @@ _cairo_win32_device_get (void)
 {
     cairo_win32_device_t *device;
 
+    CAIRO_MUTEX_INITIALIZE ();
+
     if (__cairo_win32_device)
 	return cairo_device_reference (__cairo_win32_device);