NetBSD mi_reallocarr should update errno (based on PR #499 by @devexen)

Author: daanx

src/alloc-posix.c

@@ -103,7 +103,10 @@ void* mi_reallocarray( void* p, size_t count, size_t size ) mi_attr_noexcept {
 
 int mi_reallocarr( void* p, size_t count, size_t size ) mi_attr_noexcept { // NetBSD
   mi_assert(p != NULL);
-  if (p == NULL) return EINVAL;  // should we set errno as well?
+  if (p == NULL) {
+    errno = EINVAL;
+    return EINVAL;
+  }
   void** op = (void**)p;  
   void* newp = mi_reallocarray(*op, count, size);
   if (mi_unlikely(newp == NULL)) return errno;