Kernel: Fix shadow 12GiB reserved entry when running QEMU without KVM on

Fix inspired by: https://github.com/serenityos/serenity/pull/16345

README.md

@@ -70,8 +70,6 @@ You can choose between 3 run scripts:
 
 `tools/debug.sh` will run Luna in QEMU with a port open for GDB to connect to. (run `tools/build-debug.sh`, `tools/gdb.sh`, and then `tools/debug.sh` in a separate terminal for an optimal debugging experience)
 
-Beware that running without hardware acceleration does some weird stuff with the memory map, which is why I don't use it that often.
-
 Essentially, since `run.sh` builds the toolchain if it hasn't been built, builds Luna if it hasn't been built, and runs it, you could just checkout this repo, run `run.sh`, and you're done. No need for the other scripts. Those are included for more fine-grained control/building step-by-step.
 
 You can pass any arguments you want to the run scripts, and those will be forwarded to QEMU. Example: `tools/run.sh -m 512M -net none -machine q35`.

kernel/src/memory/MemoryMap.cpp

@@ -43,7 +43,17 @@ Option<MemoryMapEntry> MemoryMapIterator::at(usize index) const
 
 Option<MemoryMapEntry> MemoryMapIterator::next()
 {
-    return at(m_cur_ent++);
+    auto entry = TRY(at(m_cur_ent++));
+
+#ifdef ARCH_X86_64
+    // Workaround for https://gitlab.com/qemu-project/qemu/-/commit/8504f129450b909c88e199ca44facd35d38ba4de
+    // This invalid 12GiB reserved entry is made up by QEMU (doesn't appear on any real hardware), so we can simply
+    // ignore it and move on to the next entry.
+    if (entry.address() == 0x000000fd00000000 && entry.size() == (0x000000ffffffffff - 0x000000fd00000000) + 1)
+        return at(m_cur_ent++);
+#endif
+
+    return entry;
 }
 
 MemoryMapEntry MemoryMapIterator::largest_free()