Kernel: Fix safe_memset not setting the last few bytes in some cases

Because the remainder variable will always be 0 unless a fault happened
we should not use it to decide if we have nothing left to memset when
finishing the fast path. This caused not all bytes to be zeroed
if the size was not an exact multiple of sizeof(size_t).

Fixes #8352

Kernel/Arch/x86/common/SafeMem.cpp

@@ -148,7 +148,7 @@ NEVER_INLINE bool safe_memset(void* dest_ptr, int c, size_t n, void*& fault_at)
         if (remainder != 0)
             return false; // fault_at is already set!
         n -= size_ts * sizeof(size_t);
-        if (remainder == 0) {
+        if (n == 0) {
             fault_at = nullptr;
             return true;
         }