qemu: Fix NULL pointer access in qemuProcessInitCpuAffinity()

Commit 2f2254c7 attempted to fix a memory leak by ensuring
cpumapToSet is always a freshly allocated bitmap, but regrettably
introduced a NULL pointer access while doing so, because it called
virBitmapCopy() without allocating the destination bitmap first.

Solve the issue by using virBitmapNewCopy() instead.
Reported-by: NJohn Ferlan <jferlan@redhat.com>
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/qemu/qemu_process.c

@@ -2498,7 +2498,7 @@ qemuProcessInitCpuAffinity(virDomainObjPtr vm)
         if (virNumaNodesetToCPUset(nodeset, &cpumapToSet) < 0)
             return -1;
     } else if (vm->def->cputune.emulatorpin) {
-        if (virBitmapCopy(cpumapToSet, vm->def->cputune.emulatorpin) < 0)
+        if (!(cpumapToSet = virBitmapNewCopy(vm->def->cputune.emulatorpin)))
             return -1;
     } else {
         if (qemuProcessGetAllCpuAffinity(&cpumapToSet) < 0)