qemuDomainChrInsertPreAlloced: Fix adding implicit console

qemuDomainChrInsertPreAlloced: Fix adding implicit console

When hotpluging a <serial/> device, we might need to add a
<console/> device with it (because of some crazy backcompat).
Now, hotplugging is done in several phases. In one of them,
qemuDomainChrPreInsert() allocates space for both devices, and
then qemuDomainChrInsertPreAlloced() actually inserts the device
into domain definition and sets up the <console/> device with it.
Except, the condition that checks whether to create the aliased
<console/> is wrong as it compares nconsoles against 0.
Surprisingly, qemuDomainChrInsertPreAllocCleanup() doesn't suffer
from the same error.

Fixes: daf51be5f1b0f7b41c0813d43d6b66edfbe4f6d9
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>