glxcmds: glXGetFBConfigs, fix screen bounds

glxcmds: glXGetFBConfigs, fix screen bounds

Bounds of screen are 0 (inclusive) and ScreenCount(dpy) (exclusive).
The upper bound was too ScreenCount(dpy) (inclusive).

This causes a crash invoked by java3d which passes down an invalid
screen:
6  0x00007f0e5198ba70 in <signal handler called> () at /lib64/libc.so.6
7  0x00007f0e14531e14 in glXGetFBConfigs (dpy=<optimized out>, screen=1, nelements=nelements@entry=0x7f0dab3c522c) at glxcmds.c:1660
8  0x00007f0e14532f7f in glXChooseFBConfig (dpy=<optimized out>, screen=<optimized out>, attribList=0x7f0dab3c54e0, nitems=0x7f0dab3c535c) at glxcmds.c:1611
9  0x00007f0e1478d29b in find_S_FBConfigs () at /usr/lib64/libj3dcore-ogl.so
10 0x00007f0e1478d3dc in find_S_S_FBConfigs () at /usr/lib64/libj3dcore-ogl.so
11 0x00007f0e1478d567 in find_AA_S_S_FBConfigs () at /usr/lib64/libj3dcore-ogl.so
12 0x00007f0e1478d728 in find_DB_AA_S_S_FBConfigs () at /usr/lib64/libj3dcore-ogl.so
13 0x00007f0e1478d97c in Java_javax_media_j3d_X11NativeConfigTemplate3D_chooseOglVisual () at /usr/lib64/libj3dcore-ogl.so

While ScreenCount(dpy) is actually 1:
(gdb) p dpy->nscreens
$2 = 1
screen=1 is passed to glXGetFBConfigs.

Fix this typo in glXGetFBConfigs.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95456
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>