Fix: Handle incoming labels with invalid UTF-8 (#1131)

It's possible that incoming labels will contain invalid UTF-8 characters. This results in a panic. This fix sanitizes the label's string to ensure only valid UTF-8 characters are included, by replacing invalid characters with � (REPLACEMENT CHARACTER)

Signed-off-by: Cooper Worobetz <cooper@worobetz.ca>

Author: vancwo

cmd/postgres_exporter/util.go

@@ -159,7 +159,7 @@ func dbToString(t interface{}) (string, bool) {
 		// Try and convert to string
 		return string(v), true
 	case string:
-		return v, true
+		return strings.ToValidUTF8(v, "�"), true
 	case bool:
 		if v {
 			return "true", true