[PRISM] Fix popped on DefinedNode

prism_compile.c

@@ -1262,7 +1262,9 @@ pm_compile_defined_expr(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *con
     lfinish[0] = NEW_LABEL(lineno);
     lfinish[1] = 0;
 
-    pm_compile_defined_expr0(iseq, node, ret, src, popped, scope_node, dummy_line_node, lineno, in_condition, lfinish);
+    if (!popped) {
+        pm_compile_defined_expr0(iseq, node, ret, src, popped, scope_node, dummy_line_node, lineno, in_condition, lfinish);
+    }
 
     if (lfinish[1]) {
         ELEM_INSERT_NEXT(last, &new_insn_body(iseq, &dummy_line_node, BIN(putnil), 0)->link);

test/ruby/test_compile_prism.rb

@@ -89,7 +89,6 @@ module Prism
     end
 
     def test_DefinedNode
-=begin
       assert_prism_eval("defined? nil")
       assert_prism_eval("defined? self")
       assert_prism_eval("defined? true")
@@ -140,7 +139,6 @@ module Prism
       assert_prism_eval("x = 1; defined? x ||= 1")
 
       assert_prism_eval("if defined? A; end")
-=end
     end
 
     def test_GlobalVariableReadNode