matrix-stack: init cache->flipped
matrix-stack: init cache->flipped

This ensures we initialize the value of cache->flipped in
_cogl_matrix_entry_cache_init()

Reviewed-by: Neil Roberts <neil@linux.intel.com>

(cherry picked from commit 507814d27298231c9ae50d74b386fb00f0909922)

Distrotech/cogl,Distrotech/cogl,Distrotech/cogl,Distrotech/cogl