Remove a level of nesting

This code should only bother running if `err != nil`, makes it easier to
understand and removes a level of nesting.

cmd/boot-script-service/default_api.go

@@ -628,22 +628,23 @@ func buildBootScript(bd BootData, sp scriptParams, chain, role, subRole, descr s
 	}
 	u := bd.Kernel.Path
 	u, err = checkURL(u)
-	if err == nil {
-		script += "kernel --name kernel " + u + " " + strings.Trim(params, " ")
-		script += " || goto boot_retry\n"
-		if bd.Initrd.Path != "" {
-			u, err = checkURL(bd.Initrd.Path)
-			if err == nil {
-				script += "initrd --name initrd " + u + " || goto boot_retry\n"
-                script += "imgstat || echo Could not show image information."
-			}
-		}
-		script += "boot || goto boot_retry\n:boot_retry\n"
-		// We could vary the length of the sleep based on retry count or some
-		// other criteria.
-		// For now, just sleep a bit
-		script += fmt.Sprintf("sleep %d\n", retryDelay) + chain + "\n"
-	}
+	if err != nil {
+	    return script, err
+	}
+    script += "kernel --name kernel " + u + " " + strings.Trim(params, " ")
+    script += " || goto boot_retry\n"
+    if bd.Initrd.Path != "" {
+        u, err = checkURL(bd.Initrd.Path)
+        if err == nil {
+            script += "initrd --name initrd " + u + " || goto boot_retry\n"
+            script += "imgstat || echo Could not show image information."
+        }
+    }
+    script += "boot || goto boot_retry\n:boot_retry\n"
+    // We could vary the length of the sleep based on retry count or some
+    // other criteria.
+    // For now, just sleep a bit
+    script += fmt.Sprintf("sleep %d\n", retryDelay) + chain + "\n"
 	return script, err
 }