Rust: Replace getBlockChildNode with uses of getStmtOrExpr.

Author: geoffw0

rust/ql/lib/codeql/rust/controlflow/internal/ControlFlowGraphImpl.qll

@@ -266,23 +266,16 @@ module ExprTrees {
     }
   }
 
-  private AstNode getBlockChildNode(BlockExpr b, int i) {
-    result = b.getStmtList().getStatement(i)
-    or
-    i = b.getStmtList().getNumberOfStatements() and
-    result = b.getStmtList().getTailExpr()
-  }
-
   class AsyncBlockExprTree extends StandardTree, PreOrderTree, PostOrderTree, AsyncBlockExpr {
-    override AstNode getChildNode(int i) { result = getBlockChildNode(this, i) }
+    override AstNode getChildNode(int i) { result = this.getStmtList().getStmtOrExpr(i) }
 
     override predicate propagatesAbnormal(AstNode child) { none() }
   }
 
   class BlockExprTree extends StandardPostOrderTree, BlockExpr {
     BlockExprTree() { not this.isAsync() }
 
-    override AstNode getChildNode(int i) { result = getBlockChildNode(this, i) }
+    override AstNode getChildNode(int i) { result = this.getStmtList().getStmtOrExpr(i) }
 
     override predicate propagatesAbnormal(AstNode child) { child = this.getChildNode(_) }
   }