C#: Fix missing phi flow

Author: hvitved

csharp/ql/src/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll

@@ -292,8 +292,8 @@ module LocalFlow {
    */
   private predicate localFlowSsaInput(Node nodeFrom, Ssa::Definition def, Ssa::Definition next) {
     exists(ControlFlow::BasicBlock bb, int i | SsaImpl::lastRefBeforeRedef(def, bb, i, next) |
-      def = nodeFrom.(SsaDefinitionNode).getDefinition() and
-      def.definesAt(_, bb, i)
+      def.definesAt(_, bb, i) and
+      def = getSsaDefinition(nodeFrom)
       or
       nodeFrom.asExprAtNode(bb.getNode(i)) instanceof AssignableRead
     )

csharp/ql/test/library-tests/dataflow/delegates/DelegateFlow.expected

@@ -25,3 +25,4 @@ delegateCall
 | DelegateFlow.cs:89:35:89:37 | delegate call | DelegateFlow.cs:74:17:74:19 | M12 | DelegateFlow.cs:92:13:92:15 | delegate creation of type MyDelegate |
 | DelegateFlow.cs:89:35:89:37 | delegate call | DelegateFlow.cs:93:13:93:21 | (...) => ... | DelegateFlow.cs:93:13:93:21 | (...) => ... |
 | DelegateFlow.cs:132:9:132:11 | delegate call | DelegateFlow.cs:131:17:131:24 | (...) => ... | file://:0:0:0:0 | <empty> |
+| DelegateFlow.cs:132:9:132:11 | delegate call | DelegateFlow.cs:135:29:135:36 | (...) => ... | DelegateFlow.cs:135:29:135:36 | (...) => ... |