Extend changes to calloc and handle in realloc

the fact that malloc may now fail.

Author: petr-bauch

src/ansi-c/library/stdlib.c

@@ -75,6 +75,10 @@ __CPROVER_HIDE:;
   __CPROVER_size_t alloc_size = nmemb * size;
 #pragma CPROVER check pop
 
+  __CPROVER_bool should_malloc_fail = __VERIFIER_nondet___CPROVER_bool();
+  if(__CPROVER_malloc_may_fail && should_malloc_fail)
+    return (void *)0;
+
   void *malloc_res;
   // realistically, calloc may return NULL,
   // and __CPROVER_allocate doesn't, but no one cares
@@ -430,7 +434,8 @@ inline void *realloc(void *ptr, __CPROVER_size_t malloc_size)
   // this shouldn't move if the new size isn't bigger
   void *res;
   res=malloc(malloc_size);
-  __CPROVER_array_copy(res, ptr);
+  if(res != (void *)0)
+    __CPROVER_array_copy(res, ptr);
   free(ptr);
 
   return res;