kernel/heap: Check for multiplication overflows in calloc.

Logic inspired by musl's.

src/system/kernel/heap.cpp

@@ -2482,6 +2482,9 @@ realloc(void *address, size_t newSize)
 void *
 calloc(size_t numElements, size_t size)
 {
+	if (size != 0 && numElements > (((size_t)(-1)) / size))
+		return NULL;
+
 	void *address = malloc(numElements * size);
 	if (address != NULL)
 		memset(address, 0, numElements * size);