[browser] Fix ConvertDllsToWebCil stack dump on bad input to be error message with input path

src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/ConvertDllsToWebCil.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Collections.Generic;
 using System.IO;
 using Microsoft.Build.Framework;
@@ -59,6 +60,24 @@ public override bool Execute()
                 continue;
             }
 
+            try
+            {
+                TaskItem webcilItem = ConvertDll(tmpDir, candidate);
+                webCilCandidates.Add(webcilItem);
+            }
+            catch (Exception ex)
+            {
+                Log.LogError($"Failed to convert '{candidate.ItemSpec}' to webcil: {ex.Message}");
+                return false;
+            }
+        }
+
+        WebCilCandidates = webCilCandidates.ToArray();
+        return true;
+    }
+
+    private TaskItem ConvertDll(string tmpDir, ITaskItem candidate)
+    {
         var dllFilePath = candidate.ItemSpec;
         var webcilFileName = Path.GetFileNameWithoutExtension(dllFilePath) + Utils.WebcilInWasmExtension;
         string candidatePath = candidate.GetMetadata("AssetTraitName") == "Culture"
@@ -101,10 +120,6 @@ public override bool Execute()
             Log.LogMessage(MessageImportance.Low, $"Changing related asset of {webcilItem} to {relatedAsset}.");
         }
 
-            webCilCandidates.Add(webcilItem);
-        }
-
-        WebCilCandidates = webCilCandidates.ToArray();
-        return true;
+        return webcilItem;
     }
 }