[fix](memory) Fix hash table buf initialize null pointer (#21315)

When compiling FunctionArrayEnumerateUniq::_execute_by_hash, AllocatorWithStackMemory::free(buf)
will be called when delete HashMapContainer. the gcc compiler will think that size > N and buf is not heap memory,
and report an error ' void free(void*)' called on unallocated object 'hash_map'

This only fails on doris docker + gcc 11.1, no problem on doris docker + clang 16.0.1,
no problem on ldb_toolchanin gcc 11.1 and clang 16.0.1.

be/src/vec/common/hash_table/hash_table.h

@@ -445,8 +445,8 @@ protected:
     using Self = HashTable;
     using cell_type = Cell;
 
-    size_t m_size = 0; /// Amount of elements
-    Cell* buf;         /// A piece of memory for all elements except the element with zero key.
+    size_t m_size = 0;   /// Amount of elements
+    Cell* buf {nullptr}; /// A piece of memory for all elements except the element with zero key.
     Grower grower;
     int64_t _resize_timer_ns;
 

be/src/vec/functions/array/function_array_enumerate_uniq.cpp

@@ -105,6 +105,16 @@ public:
         return return_type;
     }
 
+// When compiling `FunctionArrayEnumerateUniq::_execute_by_hash`, `AllocatorWithStackMemory::free(buf)`
+// will be called when `delete HashMapContainer`. the gcc compiler will think that `size > N` and `buf` is not heap memory,
+// and report an error `' void free(void*)' called on unallocated object 'hash_map'`
+// This only fails on doris docker + gcc 11.1, no problem on doris docker + clang 16.0.1,
+// no problem on ldb_toolchanin gcc 11.1 and clang 16.0.1.
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfree-nonheap-object"
+#endif // __GNUC__
+
     Status execute_impl(FunctionContext* context, Block& block, const ColumnNumbers& arguments,
                         size_t result, size_t input_rows_count) override {
         ColumnRawPtrs data_columns(arguments.size());
@@ -285,6 +295,10 @@ private:
     }
 };
 
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif // __GNUC__
+
 void register_function_array_enumerate_uniq(SimpleFunctionFactory& factory) {
     factory.register_function<FunctionArrayEnumerateUniq>();
 }