[installd] Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239

(cherry picked from commit e7bf377d62141c27508b28513e2091a826ad7b15)

Merged-In: I9dc0c1020993ec3c7e95ab552f7620ea2badf742
Change-Id: I1937de4d243e213c36f6f9c3e67380f019c6e61c
diff --git a/cmds/installd/installd.cpp b/cmds/installd/installd.cpp
index 95ed2ff..673ff0d 100644
--- a/cmds/installd/installd.cpp
+++ b/cmds/installd/installd.cpp
@@ -107,7 +107,7 @@
         DIR *dir;
         struct dirent *dirent;
         dir = opendir("/data/user");
-        if (dir != NULL) {
+        if (dir != nullptr) {
             while ((dirent = readdir(dir))) {
                 const char *name = dirent->d_name;
 
@@ -146,10 +146,10 @@
             closedir(dir);
 
             if (access(keychain_added_dir, F_OK) == 0) {
-                delete_dir_contents(keychain_added_dir, 1, 0);
+                delete_dir_contents(keychain_added_dir, 1, nullptr);
             }
             if (access(keychain_removed_dir, F_OK) == 0) {
-                delete_dir_contents(keychain_removed_dir, 1, 0);
+                delete_dir_contents(keychain_removed_dir, 1, nullptr);
             }
         }