LibC: Fix invalid 1-byte read I introduced in dirent.

When attempting to fix the dirent code I also changed
this to use strlcpy instead of the custom string copy
loop that was there before. Looking over strlcpy it
looked like it should work when using a non null terminated
string, I obviously misinterpreted the implementation
as it will read till it finds a null terminator.

Manually null terminate the string to address this.

Gunnar found this after he fixed UserspaceEmulator.
I reproduced it locally using his branch, and also
found the memory leak I had in the unit test for the
scandir that I added, so lets fix that as well.

Reported-by: Gunnar Beutner <gbeutner@serenityos.org>

Userland/Tests/LibC/TestLibCDirEnt.cpp

@@ -19,7 +19,6 @@ TEST_CASE(scandir_basic_scenario)
     for (auto i = 0; i < entries; i++) {
         if (strcmp(namelist[i]->d_name, "passwd") == 0) {
             found_passwd = true;
-            break;
         }
         free(namelist[i]);
     }