[wasm][bcl] Fix `System.Diagnostics.Trace.TraceError` crash. (#17509)

* Fix `System.Diagnostics.Trace.TraceError` crash.

- WASM does not have access to the command line arguments through the browser so the length is 0 causing index out of range error.
- The zero index of the command line arguments is what decides the `AppName` so under WASM the AppName will be blanks.

* Address review comments

* Remove #ifdef for WASM only.

- Addresses review note.
- As per channel discussion some embedding scenarios might be the same.

1 files changed, 6 insertions, 1 deletions

diff --git a/mcs/class/referencesource/System/compmod/system/diagnostics/TraceInternal.cs b/mcs/class/referencesource/System/compmod/system/diagnostics/TraceInternal.cs
index 1ff316c4c44..9e91d89e988 100644
--- a/mcs/class/referencesource/System/compmod/system/diagnostics/TraceInternal.cs
+++ b/mcs/class/referencesource/System/compmod/system/diagnostics/TraceInternal.cs
@@ -67,7 +67,12 @@ namespace System.Diagnostics {
 #if MONO_FEATURE_CAS
                     new EnvironmentPermission(EnvironmentPermissionAccess.Read, "Path").Assert();
 #endif
-                    appName = Path.GetFileName(Environment.GetCommandLineArgs()[0]);
+                    // Make sure we have command line arguments before accessing them
+                    // prevents index out of range exception.
+                    // For example Wasm does not have access to command line arguments through browser
+                    var clArgs = Environment.GetCommandLineArgs();
+                    if (clArgs.Length > 0)
+                        appName = Path.GetFileName(clArgs[0]);
                 }
                 return appName;
             }