regions_mm: vmh_free: Prevent null pointer dereference

The vmh_free function may have referenced a null pointer if an invalid
pointer was passed to it. Before referencing the allocator array item,
check if it has been initialized.

Signed-off-by: Adrian Warecki <adrian.warecki@intel.com>

Author: softwarecki

zephyr/lib/regions_mm.c

@@ -571,6 +571,9 @@ int vmh_free(struct vmh_heap *heap, void *ptr)
 	for (mem_block_iter = 0, ptr_range_found = false;
 		mem_block_iter < MAX_MEMORY_ALLOCATORS_COUNT;
 		mem_block_iter++) {
+		if (!heap->physical_blocks_allocators[mem_block_iter])
+			continue;
+
 		block_size =
 			1 << heap->physical_blocks_allocators[mem_block_iter]->info.blk_sz_shift;