I am seeing the following crash when trying to take a screenshot of a non-maximized window, using `gnome-screenshot -w`.

It works for maximized windows.

I am using the "awesome window manager" on Ubuntu.

The backtrace is from current Git master @20e885e6, but I've first noticed it with version 3.10.1-0ubuntu1.

    Program received signal SIGSEGV, Segmentation fault.
    screenshot_fallback_get_pixbuf (rectangle=<optimized out>) at screenshot-utils.c:508
    508	                      *dest_pixels++ = *src_pixels++;
    (gdb) bt
    #0  screenshot_fallback_get_pixbuf (rectangle=<optimized out>) at screenshot-utils.c:508
    #1  screenshot_get_pixbuf (rectangle=rectangle@entry=0x0) at screenshot-utils.c:660
    #2  0x0000000000408951 in finish_prepare_screenshot (self=0x62b120, rectangle=rectangle@entry=0x0)
        at screenshot-application.c:497
    #3  0x0000000000408b69 in prepare_screenshot_timeout (user_data=<optimized out>)
        at screenshot-application.c:595
    #4  0x00007ffff5f29ce5 in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
    #5  0x00007ffff5f2a048 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
    #6  0x00007ffff5f2a0ec in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
    #7  0x00007ffff6a0867c in g_application_run () from /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
    #8  0x00000000004080f5 in main (argc=2, argv=0x7fffffffbfe8) at gnome-screenshot.c:47
    (gdb) l
    503	                              + y * gdk_pixbuf_get_rowstride (tmp)
    504	                              + rec_x * 4;
    505
    506	                  for (x = 0; x < rec_width; x++)
    507	                    {
    508	                      *dest_pixels++ = *src_pixels++;
    509	                      *dest_pixels++ = *src_pixels++;
    510	                      *dest_pixels++ = *src_pixels++;
    511
    512	                      if (has_alpha)