LibLine: Fix writing to temporary file in ^X^E handler

I have no idea how this _ever_ worked, and I also have no idea why past
me didn't use FileStream to begin with.
Fixes the issue where lots of junk data would be written to the temp
file, causing the external editor to crash.

Userland/Libraries/LibLine/InternalFunctions.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/FileStream.h>
 #include <AK/ScopeGuard.h>
 #include <AK/ScopedValueRollback.h>
 #include <AK/StringBuilder.h>
@@ -527,15 +528,15 @@ void Editor::edit_in_external_editor()
             return;
         }
 
+        OutputFileStream stream { fp };
+
         StringBuilder builder;
         builder.append(Utf32View { m_buffer.data(), m_buffer.size() });
-        auto view = builder.string_view();
-        size_t remaining_size = view.length();
-
-        while (remaining_size > 0)
-            remaining_size = fwrite(view.characters_without_null_termination() - remaining_size, sizeof(char), remaining_size, fp);
-
-        fclose(fp);
+        auto bytes = builder.string_view().bytes();
+        while (!bytes.is_empty()) {
+            auto nwritten = stream.write(bytes);
+            bytes = bytes.slice(nwritten);
+        }
     }
 
     ScopeGuard remove_temp_file_guard {