fix a dead-lock in eglMakeCurrent

this was introduced in a recent change. eglMakeCurrent can
end up calling eglDestroyImageKHR via ANativewWindow::disconnect
when the consumer is in the same process.

we make sure we don't hold the lock while this is happening.

Change-Id: Id17fe4fd76eecf5f962cefb9aa32be41fc1b042d