fix: keep empty string result in file dialog placeholder functions

Co-authored-by: 7474 <4744735+7474@users.noreply.github.com>

Author: Copilot

SRC.Sharp/SRCCore/Expressions/Functions/File.cs

@@ -147,7 +147,6 @@ protected override ValueType InvokeInternal(SRC SRC, ValueType etype, string[] @
 
             if (etype == ValueType.StringType)
             {
-                str_result = GeneralLib.FormatNum(num_result);
                 return ValueType.StringType;
             }
             else
@@ -230,7 +229,6 @@ protected override ValueType InvokeInternal(SRC SRC, ValueType etype, string[] @
 
             if (etype == ValueType.StringType)
             {
-                str_result = GeneralLib.FormatNum(num_result);
                 return ValueType.StringType;
             }
             else
@@ -239,4 +237,4 @@ protected override ValueType InvokeInternal(SRC SRC, ValueType etype, string[] @
             }
         }
     }
-}
+}

SRC.Sharp/SRCCoreTests/Expressions/FileFunctionTests.cs

@@ -0,0 +1,44 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using SRCCore.Expressions.Functions;
+using SRCCore.TestLib;
+
+namespace SRCCore.Expressions.Tests
+{
+    [TestClass]
+    public class FileFunctionTests
+    {
+        private static SRC CreateSrc()
+        {
+            return new SRC
+            {
+                GUI = new MockGUI(),
+            };
+        }
+
+        [TestMethod]
+        public void Loadfiledialog_StringType_DefaultResultIsEmptyString()
+        {
+            var src = CreateSrc();
+            var sut = new Loadfiledialog();
+
+            var resultType = sut.Invoke(src, ValueType.StringType, new string[1], 0, new bool[1], out var strResult, out var numResult);
+
+            Assert.AreEqual(ValueType.StringType, resultType);
+            Assert.AreEqual("", strResult);
+            Assert.AreEqual(0d, numResult);
+        }
+
+        [TestMethod]
+        public void Savefiledialog_StringType_DefaultResultIsEmptyString()
+        {
+            var src = CreateSrc();
+            var sut = new Savefiledialog();
+
+            var resultType = sut.Invoke(src, ValueType.StringType, new string[1], 0, new bool[1], out var strResult, out var numResult);
+
+            Assert.AreEqual(ValueType.StringType, resultType);
+            Assert.AreEqual("", strResult);
+            Assert.AreEqual(0d, numResult);
+        }
+    }
+}