fix: Moved padding declaration in arena_ensure_capacity

descripcion mas detallada

src/arena.c

@@ -93,12 +93,11 @@ ArenaErr arena_ensure_capacity(Arena *arena, size_t size, size_t alignment) {
         return ARENA_NULL_ARG;
     }
 
+    SizeResult padding = get_arena_align_padding(arena, alignment);
+    if (!padding.is_valid) {
+        return padding.err;
+    }
     while (true) {
-        SizeResult padding = get_arena_align_padding(arena, alignment);
-        if (!padding.is_valid) {
-            return padding.err;
-        }
-
         if (arena->offset > SIZE_MAX - padding.val - size) {
             return ARENA_CAPACITY_OVERFLOW;
         }