C#: Introduce Argument and Parameter index validation for models.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/dataflow/ExternalFlow.qll

@@ -173,6 +173,8 @@ module ModelValidation {
         or
         part = input.getToken(_) and
         parseParam(part, _)
+        or
+        invalidIndexComponent(input, part)
       ) and
       result = "Unrecognized input specification \"" + part + "\" in " + pred + " model."
     )
@@ -184,9 +186,13 @@ module ModelValidation {
       or
       summaryModel(_, _, _, _, _, _, _, output, _, _) and pred = "summary"
     |
-      invalidSpecComponent(output, part) and
-      not part = "" and
-      not (part = ["Argument", "Parameter"] and pred = "source") and
+      (
+        invalidSpecComponent(output, part) and
+        not part = "" and
+        not (part = ["Argument", "Parameter"] and pred = "source")
+        or
+        invalidIndexComponent(output, part)
+      ) and
       result = "Unrecognized output specification \"" + part + "\" in " + pred + " model."
     )
   }