r262589 introduced another instance of the bug fixed in r258131.

2018-07-23  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR tree-optimization/86618
	* tree-vect-stmts.c (vectorizable_call): Don't take the address
	of LOOP_VINFO_MASKS (loop_vinfo) when loop_vinfo is null.

From-SVN: r262951