Fix NPE in IdenticalExpressionsDiagnostic when ctx.children is null

Co-authored-by: nixel2007 <1132840+nixel2007@users.noreply.github.com>

Author: Copilot

src/main/java/com/github/_1c_syntax/bsl/languageserver/diagnostics/IdenticalExpressionsDiagnostic.java

@@ -235,6 +235,6 @@ private static boolean isComplementary(BinaryOperationNode binary) {
   }
 
   private static boolean sufficientSize(BSLParser.ExpressionContext ctx) {
-    return ctx.children.size() < MIN_EXPRESSION_SIZE;
+    return ctx.children == null || ctx.children.size() < MIN_EXPRESSION_SIZE;
   }
 }