LibCore: Make get_current_user_home_path() return String & close passwd

This API was returning a "const char*" and it was unclear who took care
of the underlying memory. Returning a String makes that obvious.

Also make sure we close the /etc/passwd file when we're done with it.

Applications/Launcher/main.cpp

@@ -24,7 +24,9 @@ void handle_sigchld(int)
 
 int main(int argc, char** argv)
 {
-    chdir(get_current_user_home_path());
+    if (chdir(get_current_user_home_path().characters()) < 0)
+        perror("chdir");
+
     GApplication app(argc, argv);
 
     signal(SIGCHLD, handle_sigchld);

Applications/Terminal/main.cpp

@@ -133,7 +133,8 @@ int main(int argc, char** argv)
 {
     GApplication app(argc, argv);
 
-    chdir(get_current_user_home_path());
+    if (chdir(get_current_user_home_path().characters()) < 0)
+        perror("chdir");
 
     int ptm_fd = open("/dev/ptmx", O_RDWR);
     if (ptm_fd < 0) {

Libraries/LibCore/CUserInfo.cpp

@@ -3,15 +3,13 @@
 #include <stdlib.h>
 #include <unistd.h>
 
-const char* get_current_user_home_path()
+String get_current_user_home_path()
 {
     if (auto* home_env = getenv("HOME"))
         return home_env;
 
-    auto d = "/";
-    uid_t uid = getuid();
-    if (auto* pwd = getpwuid(uid))
-        return pwd->pw_dir;
-
-    return d;
+    auto* pwd = getpwuid(getuid());
+    String path = pwd ? pwd->pw_dir : "/";
+    endpwent();
+    return path;
 }

Libraries/LibCore/CUserInfo.h

@@ -1 +1,5 @@
-const char* get_current_user_home_path();
+#pragma once
+
+#include <AK/AKString.h>
+
+String get_current_user_home_path();