Handle NULL pointers in base arena

mem/src/arena/mem_arena.c

@@ -26,6 +26,10 @@ internal void base_arena_clear(BaseArena *arena);
 internal void base_arena_free(BaseArena *arena);
 
 internal bool base_arena_init(BaseArena *arena, u64 capacity) {
+  if (!arena || arena->buf) {
+    return false;
+  }
+
   u64 alloc_size = sizeof(u8) * capacity;
 
   arena->buf = (u8 *)malloc(alloc_size);
@@ -47,6 +51,10 @@ internal void *base_arena_alloc(BaseArena *arena, u64 size) {
 
 internal void *base_arena_alloc_aligned(BaseArena *arena, u64 size,
                                         u64 alignment) {
+  if (!arena) {
+    return NULL;
+  }
+
   u8 *output = mem_util_align_forward((void *)(arena->offset), alignment);
   if (output + size >= arena->buf + arena->capacity) {
     return NULL;
@@ -58,11 +66,19 @@ internal void *base_arena_alloc_aligned(BaseArena *arena, u64 size,
 }
 
 internal void base_arena_clear(BaseArena *arena) {
+  if (!arena) {
+    return;
+  }
+
   memset(arena->buf, 0, arena->offset - arena->buf);
   arena->offset = arena->buf;
 }
 
 internal void base_arena_free(BaseArena *arena) {
+  if (!arena) {
+    return;
+  }
+
   if (arena->buf) {
     free(arena->buf);
   }