qemu: fix a segfault in qemuProcessWaitForMonitor
qemu: fix a segfault in qemuProcessWaitForMonitor

Commit b3f2b4ca5cfe98b08ffdb96f0455e3e333e5ace6 left buf unallocated in
the case of QMP capability probing being used, leading to a segfault in
strlen in the cleanup path.

This patch opens the log and allocates the buffer if QMP probing was
used, so we can display the helpful error message.

elmarco/libvirt,taget/libvirt,zippy2/libvirt,iam-TJ/libvirt,rlaager/libvirt,trainstack/libvirt,shugaoye/libvirt,cbosdo/libvirt,andreabolognani/libvirt,libvirt/libvirt,olafhering/libvirt,datto/libvirt,cbosdo/libvirt,taget/libvirt,VenkatDatta/libvirt,iam-TJ/libvirt,zhlcindy/libvirt-1.1.4-maintain,trainstack/libvirt,crobinso/libvirt,jfehlig/libvirt,zhlcindy/libvirt-1.1.4-maintain,cbosdo/libvirt,libvirt/libvirt,eskultety/libvirt,jardasgit/libvirt,zhlcindy/libvirt-1.1.4-maintain,andreabolognani/libvirt,nertpinx/libvirt,iam-TJ/libvirt,zippy2/libvirt,trainstack/libvirt,elmarco/libvirt,crobinso/libvirt,taget/libvirt,eskultety/libvirt,olafhering/libvirt,datto/libvirt,jardasgit/libvirt,bjzhang/libvirt,olafhering/libvirt,eskultety/libvirt,zippy2/libvirt,bjzhang/libvirt,siboulet/libvirt-openvz,rlaager/libvirt,fabianfreyer/libvirt,siboulet/libvirt-openvz,zippy2/libvirt,rlaager/libvirt,jfehlig/libvirt,elmarco/libvirt,nertpinx/libvirt,nertpinx/libvirt,andreabolognani/libvirt,siboulet/libvirt-openvz,iam-TJ/libvirt,andreabolognani/libvirt,trainstack/libvirt,fabianfreyer/libvirt,agx/libvirt,elmarco/libvirt,nertpinx/libvirt,jardasgit/libvirt,datto/libvirt,crobinso/libvirt,crobinso/libvirt,eskultety/libvirt,siboulet/libvirt-openvz,trainstack/libvirt,shugaoye/libvirt,bjzhang/libvirt,VenkatDatta/libvirt,taget/libvirt,bjzhang/libvirt,trainstack/libvirt,cbosdo/libvirt,jfehlig/libvirt,zhlcindy/libvirt-1.1.4-maintain,nertpinx/libvirt,iam-TJ/libvirt,rlaager/libvirt,datto/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,trainstack/libvirt,olafhering/libvirt,bjzhang/libvirt,jfehlig/libvirt,rlaager/libvirt,shugaoye/libvirt,agx/libvirt,andreabolognani/libvirt,iam-TJ/libvirt,elmarco/libvirt,taget/libvirt,VenkatDatta/libvirt,agx/libvirt,libvirt/libvirt,siboulet/libvirt-openvz,shugaoye/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,eskultety/libvirt,iam-TJ/libvirt,agx/libvirt,shugaoye/libvirt,datto/libvirt,libvirt/libvirt,zhlcindy/libvirt-1.1.4-maintain,jardasgit/libvirt,agx/libvirt,cbosdo/libvirt