Only add libvirt-qemu user to libvirt-qemu group once

when the group gets created

debian/libvirt-bin.postinst

@@ -23,13 +23,10 @@ add_users_groups()
         addgroup --system libvirt
     fi
 
-    # user and group libvirt runs qemu/kvm instances with
     if ! getent group kvm >/dev/null; then
         addgroup --quiet --system kvm
     fi
-    if ! getent group libvirt-qemu >/dev/null; then
-        addgroup --quiet --system libvirt-qemu
-    fi
+    # user and group libvirt runs qemu/kvm instances with
     if ! getent passwd libvirt-qemu >/dev/null; then
         adduser --quiet \
             --system \
@@ -42,7 +39,10 @@ add_users_groups()
             -gecos "Libvirt Qemu" \
             libvirt-qemu
     fi
-    adduser libvirt-qemu libvirt-qemu
+    if ! getent group libvirt-qemu >/dev/null; then
+        addgroup --quiet --system libvirt-qemu
+        adduser libvirt-qemu libvirt-qemu
+    fi
 }