When -fobjc-nilcheck is enabled, messages that result in a struct type should
yield a zero-initialized struct when sent to nil. Currently, the frontend
crashes when it encounters this situation. This patch fixes the crash by
generating the tree for the `{}` initializer.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk> Co-authored-by: Matt Jacobson <mhjacobson@me.com>
PR objc/101666