False error Fix (#2109)

* fix: use UnsetWorkspaceName for empty input in workspace rename
Previously, empty input would set workspace name to empty string,
causing issues with Niri's unique workspace name requirement.
Now uses UnsetWorkspaceName action when input is empty.

* prevent false failed to load config toast on niri validation
Move error toast logic from StdioCollector.onStreamFinished to Process.onExited
so it only displays when niri validate actually fails (non-zero exit code),
not when stderr outputs early progress messages during config processing.

quickshell/Services/NiriService.qml

@@ -99,15 +99,14 @@ Singleton {
                 const lines = text.split('\n');
                 const trimmedLines = lines.map(line => line.replace(/\s+$/, '')).filter(line => line.length > 0);
                 configValidationOutput = trimmedLines.join('\n').trim();
-                if (hasInitialConnection) {
-                    ToastService.showError("niri: failed to load config", configValidationOutput, "", "niri-config");
-                }
             }
         }
 
         onExited: exitCode => {
             if (exitCode === 0) {
                 configValidationOutput = "";
+            } else if (hasInitialConnection && configValidationOutput.length > 0) {
+                ToastService.showError("niri: failed to load config", configValidationOutput, "", "niri-config");
             }
         }
     }