internal/server/instance/drivers: Don't return an error if console lo…

…g file doesn't exist

Right at VM creation, the ring buffer for the console is empty. If you
try to access an interactive console, such as by running a command like
`incus launch images:ubuntu/24.04 v1 --vm --console`, you'd get an error
that the log file doesn't exist when attempting to save off the ring
buffer contents prior to switching to the unix socket connection. We
shouldn't return an error, but rather an empty string in this case.

Signed-off-by: Mathias Gibbens <mathias.gibbens@futurfusion.io>

internal/server/instance/drivers/driver_qemu.go

@@ -9381,6 +9381,11 @@ func (d *qemu) ConsoleLog() (string, error) {
 	// Read and return the complete log for this instance.
 	fullLog, err := os.ReadFile(d.common.ConsoleBufferLogPath())
 	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			// If there's no log file yet, such as right at VM creation, return an empty string.
+			return "", nil
+		}
+
 		return "", err
 	}