Heap: Use safe_mul in kcalloc()

kernel/src/memory/Heap.cpp

@@ -5,6 +5,7 @@
 #include "memory/KernelVM.h"
 #include "memory/MemoryManager.h"
 #include <luna/Alignment.h>
+#include <luna/SafeArithmetic.h>
 #include <luna/String.h>
 #include <luna/SystemError.h>
 
@@ -332,8 +333,7 @@ Result<void*> krealloc(void* ptr, usize size)
 
 Result<void*> kcalloc(usize nmemb, usize size)
 {
-    // FIXME: Check for overflows.
-    const usize realsize = nmemb * size;
+    const usize realsize = TRY(safe_mul(nmemb, size));
     void* const ptr = TRY(kmalloc(realsize));
     return memset(ptr, 0, realsize);
 }