Default to info level for an empty log-level

I'd assumed that the `omitempty` directive for LogLevel in
internal/config/config.go would get us this behaviour. If it did, we
wouldn't have had to specify the default twice. Unfortunately, it
doesn't, which is to say that given a config file like:

```
log_level:
```

The default *is* overridden by the empty string.

It's an easy enough fix.

Changelog: fixed

internal/logger/logger.go

@@ -22,6 +22,14 @@ func logFmt(inFmt string) string {
 	return inFmt
 }
 
+func logLevel(inLevel string) string {
+	if inLevel == "" {
+		return "info"
+	}
+
+	return inLevel
+}
+
 func logFile(inFile string) string {
 	if inFile == "" {
 		return "stderr"
@@ -35,7 +43,7 @@ func buildOpts(cfg *config.Config) []log.LoggerOption {
 		log.WithFormatter(logFmt(cfg.LogFormat)),
 		log.WithOutputName(logFile(cfg.LogFile)),
 		log.WithTimezone(time.UTC),
-		log.WithLogLevel(cfg.LogLevel),
+		log.WithLogLevel(logLevel(cfg.LogLevel)),
 	}
 }
 

internal/logger/logger_test.go

@@ -30,9 +30,11 @@ func TestConfigure(t *testing.T) {
 	tmpFile.Close()
 
 	data, err := os.ReadFile(tmpFile.Name())
+	dataStr := string(data)
 	require.NoError(t, err)
-	require.Contains(t, string(data), `msg":"this is a test"`)
-	require.NotContains(t, string(data), `msg:":"debug log message"`)
+	require.Contains(t, dataStr, `"msg":"this is a test"`)
+	require.NotContains(t, dataStr, `"msg":"debug log message"`)
+	require.NotContains(t, dataStr, `"msg":"unknown log level`)
 }
 
 func TestConfigureWithDebugLogLevel(t *testing.T) {