init: add [[nodiscard]] to Result

It's better to either check these results or explicitly ignore them.
Only a few callers weren't already doing this, so it's relatively
trivial to enforce.

Test: build
Change-Id: I44cdc342e46128f66cac914aaa0b9b4559cacd8c
diff --git a/init/keychords.cpp b/init/keychords.cpp
index b8c1cfd..f5ac44f 100644
--- a/init/keychords.cpp
+++ b/init/keychords.cpp
@@ -41,7 +41,7 @@
 
 Keychords::~Keychords() noexcept {
     if (inotify_fd_ >= 0) {
-        epoll_->UnregisterHandler(inotify_fd_);
+        epoll_->UnregisterHandler(inotify_fd_).IgnoreError();
         ::close(inotify_fd_);
     }
     while (!registration_.empty()) GeteventCloseDevice(registration_.begin()->first);
@@ -186,7 +186,11 @@
         current_ |= mask & available & set;
         LambdaCheck();
     }
-    epoll_->RegisterHandler(fd, [this, fd]() { this->LambdaHandler(fd); });
+    if (auto result = epoll_->RegisterHandler(fd, [this, fd]() { this->LambdaHandler(fd); });
+        !result) {
+        LOG(WARNING) << "Could not register keychord epoll handler: " << result.error();
+        return false;
+    }
     return true;
 }
 
@@ -208,7 +212,7 @@
     auto it = registration_.find(device);
     if (it == registration_.end()) return;
     auto fd = (*it).second;
-    epoll_->UnregisterHandler(fd);
+    epoll_->UnregisterHandler(fd).IgnoreError();
     registration_.erase(it);
     ::close(fd);
 }
@@ -266,7 +270,11 @@
     }
 
     if (inotify_fd_ >= 0) {
-        epoll_->RegisterHandler(inotify_fd_, [this]() { this->InotifyHandler(); });
+        if (auto result =
+                    epoll_->RegisterHandler(inotify_fd_, [this]() { this->InotifyHandler(); });
+            !result) {
+            LOG(WARNING) << "Could not register keychord epoll handler: " << result.error();
+        }
     }
 }