Do not overwrite glx_handle in epoxy_load_gl if GLX library is loaded already

Reviewed-by: Adam Jackson <ajax@redhat.com>

Signed-off-by: Emmanuele Bassi <ebassi@gnome.org>

src/dispatch_common.c

@@ -677,6 +677,7 @@ epoxy_load_gl(void)
     if (!api.gl_handle) {
 	get_dlopen_handle(&api.gl_handle, GLX_LIB, true, true);
 #if PLATFORM_HAS_GLX
+        if (!api.glx_handle)
 	    api.glx_handle = api.gl_handle;
 #endif
     }