Kernel: Make Inode::set_shared_vmobject() OOM-fallible

Allocating a WeakPtr can fail, so this let's us properly propagate said
failure.

Kernel/FileSystem/Inode.cpp

@@ -130,10 +130,11 @@ ErrorOr<void> Inode::decrement_link_count()
     return ENOTIMPL;
 }
 
-void Inode::set_shared_vmobject(Memory::SharedInodeVMObject& vmobject)
+ErrorOr<void> Inode::set_shared_vmobject(Memory::SharedInodeVMObject& vmobject)
 {
     MutexLocker locker(m_inode_lock);
-    m_shared_vmobject = vmobject;
+    m_shared_vmobject = TRY(vmobject.try_make_weak_ptr<Memory::SharedInodeVMObject>());
+    return {};
 }
 
 RefPtr<LocalSocket> Inode::bound_socket() const

Kernel/FileSystem/Inode.h

@@ -82,7 +82,7 @@ public:
 
     void will_be_destroyed();
 
-    void set_shared_vmobject(Memory::SharedInodeVMObject&);
+    ErrorOr<void> set_shared_vmobject(Memory::SharedInodeVMObject&);
     RefPtr<Memory::SharedInodeVMObject> shared_vmobject() const;
 
     static void sync_all();

Kernel/Memory/SharedInodeVMObject.cpp

@@ -18,7 +18,7 @@ ErrorOr<NonnullRefPtr<SharedInodeVMObject>> SharedInodeVMObject::try_create_with
     auto new_physical_pages = TRY(VMObject::try_create_physical_pages(size));
     auto dirty_pages = TRY(Bitmap::try_create(new_physical_pages.size(), false));
     auto vmobject = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) SharedInodeVMObject(inode, move(new_physical_pages), move(dirty_pages))));
-    vmobject->inode().set_shared_vmobject(*vmobject);
+    TRY(vmobject->inode().set_shared_vmobject(*vmobject));
     return vmobject;
 }