cli/debug: fix OTELErrorHandler logging messages if there's no error

I noticed this in a ticket in the compose issue tracker; with debug logging
enabled, the OTEL error-logger may be logging even if there's no error;

    DEBU[0000] Executing bake with args: [bake --file - --progress rawjson --metadata-file /tmp/compose-build-metadataFile-1203980021.json --allow fs.read=/home/user/dev/project --allow fs.read=/home/user/dev/project --allow fs.read=/home/user/dev/project/nginx --allow fs.read=/home/user/dev/project]
    TRAC[0000] Plugin server listening on @docker_cli_d8df486f78df3b7357995be71bf0cef6
    DEBU[0005] otel error                                    error="<nil>"
    ^CTRAC[0055] Closing plugin server
    TRAC[0055] Closing plugin server
    DEBU[0055] otel error                                    error="<nil>"
    DEBU[0055] otel error                                    error="<nil>"

Update the error-handler to not log if there's no error.

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

cli/debug/debug.go

@@ -33,5 +33,8 @@ func IsEnabled() bool {
 // The default is to log to the debug level which is only
 // enabled when debugging is enabled.
 var OTELErrorHandler otel.ErrorHandler = otel.ErrorHandlerFunc(func(err error) {
+	if err == nil {
+		return
+	}
 	logrus.WithError(err).Debug("otel error")
 })