[M103 merge] assistant-dlc: Avoid self-reset

When assistant is enabled and disabled/enabled again, the `dlc_library_`
could be self-reset.

(cherry picked from commit 28c5665)

Bug: b:232852357
Test: manaul
Change-Id: Ibefeaedda9c482c26e2866acecbc3c3cdb919442
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3652903
Commit-Queue: Tao Wu <wutao@chromium.org>
Reviewed-by: Yuki Awano <yawano@google.com>
Cr-Original-Commit-Position: refs/heads/main@{#1004988}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3656738
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/branch-heads/5060@{#152}
Cr-Branched-From: b83393d-refs/heads/main@{#1002911}

chromeos/services/libassistant/libassistant_service.cc

@@ -77,6 +77,8 @@ class LibassistantFactoryImpl : public LibassistantFactory {
     }
 
     base::FilePath path = GetLibassisantPath(dlc_path.value());
+    // Self-resets are not allowed on unique_ptr.
+    dlc_library_.reset();
     dlc_library_ = base::ScopedNativeLibrary(path);
     if (IsDlcLibraryValid()) {
       DVLOG(3) << "Loaded libassistant shared library from: " << path;