checker: fix fn var resolver (fix #24525) (#24542)

Author: felipensp

vlib/v/checker/checker.v

@@ -3991,7 +3991,14 @@ fn (mut c Checker) at_expr(mut node ast.AtExpr) ast.Type {
 }
 
 fn (mut c Checker) resolve_var_fn(func &ast.Fn, mut node ast.Ident, name string) ast.Type {
-	mut fn_type := ast.new_type(c.table.find_or_register_fn_type(func, false, true))
+	mut fn_type := c.table.find_or_register_fn_type(func, false, true)
+	if fn_type < 0 {
+		mut f := ast.Fn{
+			...func
+		}
+		f.name = ''
+		fn_type = c.table.find_or_register_fn_type(f, false, true)
+	}
 	if func.generic_names.len > 0 {
 		concrete_types := node.concrete_types.map(c.unwrap_generic(it))
 		if typ_ := c.table.convert_generic_type(fn_type, func.generic_names, concrete_types) {