Replace catch(NullReferenceException) with IsDefaultOrEmpty guard in AttributeDataExtensions

The NamedArguments property returns a default ImmutableArray when attribute data is
incomplete/malformed at analysis time. Guard with .IsDefaultOrEmpty before iterating
rather than swallowing NullReferenceException, which could mask real Roslyn API bugs.

Agent-Logs-Url: https://github.com/reactiveui/ReactiveUI.SourceGenerators/sessions/7c58663a-a9ce-4cfa-a3ff-9a57bc0347a9

Co-authored-by: ChrisPulman <4910015+ChrisPulman@users.noreply.github.com>

Author: Copilot

src/ReactiveUI.SourceGenerators.Roslyn/Core/Extensions/AttributeDataExtensions.cs

@@ -37,7 +37,9 @@ public static bool TryGetNamedArgument<T>(this AttributeData attributeData, stri
             return false;
         }
 
-        try
+        // NamedArguments returns a default ImmutableArray when attribute data is incomplete/malformed.
+        // Guard with IsDefaultOrEmpty rather than catching NullReferenceException to avoid masking real bugs.
+        if (!attributeData.NamedArguments.IsDefaultOrEmpty)
         {
             foreach (var properties in attributeData.NamedArguments)
             {
@@ -47,9 +49,6 @@ public static bool TryGetNamedArgument<T>(this AttributeData attributeData, stri
                 }
             }
         }
-        catch (NullReferenceException)
-        {
-        }
 
         value = default;
 
@@ -70,7 +69,9 @@ public static bool TryGetNamedArgument<T>(this AttributeData attributeData, stri
             return default;
         }
 
-        try
+        // NamedArguments returns a default ImmutableArray when attribute data is incomplete/malformed.
+        // Guard with IsDefaultOrEmpty rather than catching NullReferenceException to avoid masking real bugs.
+        if (!attributeData.NamedArguments.IsDefaultOrEmpty)
         {
             foreach (var properties in attributeData.NamedArguments)
             {
@@ -80,9 +81,6 @@ public static bool TryGetNamedArgument<T>(this AttributeData attributeData, stri
                 }
             }
         }
-        catch (NullReferenceException)
-        {
-        }
 
         return default;
     }