[jb-gw] work around a bug in supervisor returning an empty user (#18975)

Author: akosyakov

components/ide/jetbrains/gateway-plugin/src/main/kotlin/io/gitpod/jetbrains/gateway/GitpodConnectionProvider.kt

@@ -375,7 +375,7 @@ class GitpodConnectionProvider : GatewayConnectionProvider {
             }
 
             var userName = keyPair.userName
-            if (userName == null) {
+            if (userName.isNullOrBlank()) {
                 userName = "gitpod"
             }