gl_destroy_textures: do not leak textures.

glIsTexture() only works when the texture under test has been bound to a target
(thus calling glBindTexture()).

src/utils_glx.c

@@ -796,8 +796,10 @@ gl_destroy_texture(
         abort();
 
     glEnable(target);
+    glBindTexture(target, *texture);
     if (glIsTexture(*texture))
         glDeleteTextures(1, texture);
+    glBindTexture(target, 0);
     glDisable(target);
 }