This patch fixes PR96312. Cures a used uninitialized warning.

2020-08-10  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/96312
	* trans-expr.c (fcncall_realloc_result): Only compare shapes if
	lhs was allocated..

gcc/testsuite/
	PR fortran/96312
	* gfortran.dg/pr96312.f90: New test.