feat: check CurrentMemoryContext is not Bump

Many operations require memory allocations and accordingly it's freeing.
But Bump context do not have header and so can not perform some
operations including 'pfree'. So we should check and deny any allocation
sensetive operations - not only 'palloc' explicitly, but also any
functions that may use memory allocations, i.e. various 'out' functions.

Author: ashenBlade

src/variables.ts

@@ -1035,8 +1035,17 @@ function isValidMemoryContextTag(tag: string) {
         case 'T_AllocSetContext':
         case 'T_SlabContext':       /* 10 */
         case 'T_GenerationContext': /* 11 */
-        case 'T_BumpContext':       /* 17 */
             return true;
+        case 'T_BumpContext':       /* 17 */
+            /* 
+             * If we are going to perform memory allocations then we are
+             * going to free allocated memory accordingly.
+             * But Bump context does not allow pfree/repalloc/etc... operations.
+             * 
+             * We can create our own memory context to perform allocations here,
+             * but it will be hard to maintain.
+             */
+            return false;
     }
 
     /* This is T_Invalid or something else */
@@ -5870,6 +5879,8 @@ class TupleTableSlotAttributesVariable extends Variable {
     }
 
     async doGetChildren() {
+        await this.checkCanAlloc();
+        
         const nvalid = await this.slot.getMemberValueNumber('tts_nvalid');
         if (nvalid == 0) {
             return [];