fix: handle nil metadata

[tim775]

from sentry

"runtime error: invalid memory address or nil pointer dereference"

], 
"stacktrace": 
"1: running [Created by errgroup.(*Group).Go @ errgroup.go:72]
   :24                                                             Stack()
   :270                                                            (*parallelRunner).run.func1.1()
   :884                                                            panic()
   :233                                                            (*TerragruntHCLProvider).LoadResources.func2()
   :299                                                            order2_func()
   :308                                                            median_func()
   :316                                                            medianAdjacent_func()
   :279                                                            choosePivot_func()
   :89                                                             pdqsort_func()
   :23                                                             Slice()
   :232                                                            (*TerragruntHCLProvider).LoadResources()
   ...