work around a null pointer dereference error

This fixes #462.

* spot/twaalgos/gfguarantee.cc (do_g_f_terminal_inplace): Replace the
redirect_src vector by a unique_ptr<unsigned[]>.  Not only does this
remove the false positive diagnostic, but it also removes the unneeded
default initialization of the elements of that vector.
16 jobs for next in 238 minutes and 51 seconds (queued for 8 seconds)
Status Name Job ID Coverage
  Build
passed alpine-gcc #143672

00:53:37

passed arch-clang #143673

00:49:16

passed arch-gcc-glibcxxdebug #143674

01:16:06

passed debian-gcc-snapshot #143671

01:11:19

passed debian-stable-gcc #143669

01:00:47

passed debian-unstable-gcc-coverage #143670

00:34:47

90.7%
passed debpkg-stable #143677

01:21:59

passed debpkg-unstable #143678

01:11:47

passed mingw-shared #143675

00:12:05

passed mingw-static #143676

00:09:47

passed raspbian #143680
armv7

01:30:53

passed rpm-pkg #143679

01:06:56

 
  Build2
passed debpkg-stable-i386 #143681
x86

01:14:58

passed debpkg-unstable-i386 #143682
x86

00:58:28

 
  Publish
passed publish-rpm #143683
dput

00:00:47

passed publish-unstable #143684
dput

00:03:21