Skip statements with no BB in ranger.

Skip statements with no BB in ranger.

The function postfold_gcond_edges() registers relations coming out of a
GIMPLE_COND.  With upcoming changes, we may be called with statements
not in the IL (for example, dummy statements created by the
forward threader).  This patch avoids breakage by exiting if the
statement does not have a defining basic block.  There is a similar
change to the path solver.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* gimple-range-fold.cc (fold_using_range::postfold_gcond_edges):
	Skip statements with no defining BB.
	* gimple-range-path.cc (path_range_query::range_defined_in_block):
	Do not get confused by statements with no defining BB.