cgraph: Avoid segfault when attempting to dump NULL clone_info

cgraph: Avoid segfault when attempting to dump NULL clone_info

cgraph_node::materialize_clone segfaulted when I tried compiling
Tramp3D with -fdump-ipa-all because there was no clone_info - IPA-CP
created a clone only for an aggregate constant, adding a note to its
transformation summary but not creating any tree_map nor
param_adjustements.

Fixed with the following obvious extra checks which has passed
bootstrap and testing on x86_64-linux.

gcc/ChangeLog:

2020-11-12  Martin Jambor  <mjambor@suse.cz>

	* cgraphclones.c (cgraph_node::materialize_clone): Check that clone
	info is not NULL before attempting to dump it.