[utils] Re-implement safe fail behavior into AllocatorBase

When pulling from upstream develop, AllocatorBase has been moved to
utils/allocator.hpp. This commit simply re-introduces safe fail behavior
into AllocatorBase.construct and AllocatorBase.destroy that was
previously added by Matthew Arnold (see 3ed0768 for more details).

src/modm/utils/allocator.hpp

@@ -42,6 +42,7 @@ class AllocatorBase
     static inline void
     construct(T* p, const T& value)
     {
+        if (p == nullptr) return;
         // placement new
         ::new((void *) p) T(value);
     }
@@ -57,6 +58,7 @@ class AllocatorBase
     static inline void
     destroy(T* p)
     {
+        if (p == nullptr) return;
         p->~T();
     }