SurfaceTexture: fix a memory leak

This change fixes an issue where we were sometimes setting the SurfaceTexture's
EGLDisplay to EGL_NO_DISPLAY in detachFromContext, and then subsequently
abandoning the texture.  Abandoning while in the detached state would result in
the eglDestroyImageKHR calls failing, which resulted in a memory leak.

Bug: 6302694
Change-Id: I24c1de0dac029a83c7508075fb8aaeaed96a14ea