Changes based on code review

src/Compilers/CSharp/Portable/BoundTree/UnboundLambda.cs

@@ -972,18 +972,18 @@ private static int CanonicallyCompareDiagnostics(Diagnostic x, Diagnostic y)
 
             int codeCompare = xCode.CompareTo(yCode);
 
+            // Optimization: don't bother 
+            if (codeCompare != 0)
+                return codeCompare;
+
             // ToString fails for a diagnostic with an error code that does not prevent successful delegate conversion.
             // Also, the order doesn't matter, since all such diagnostics will be dropped.
-            if (!ErrorFacts.PreventsSuccessfulDelegateConversion(xCode) || !ErrorFacts.PreventsSuccessfulDelegateConversion(yCode))
+            if (!ErrorFacts.PreventsSuccessfulDelegateConversion(xCode))
             {
                 return codeCompare;
             }
 
-            // Optimization: don't bother 
-            if (codeCompare != 0)
-                return codeCompare;
-
-            for (int i = 0; i < x.Arguments.Count && i < y.Arguments.Count; i++)
+            for (int i = 0; i < Math.Min(x.Arguments.Count, y.Arguments.Count); i++)
             {
                 object argx = x.Arguments[i];
                 object argy = y.Arguments[i];