version.py: fix build_id after recent refactors (#1393)

* version.py: fix build_id after recent refactors

* fix lint

pwndbg/lib/version.py

@@ -6,8 +6,11 @@ def build_id():  # type: () -> str
     """
     Returns pwndbg commit id if git is available.
     """
+    pwndbg_dir = os.path.dirname(os.path.dirname(os.path.dirname(__file__)))
+    assert os.path.exists(os.path.join(pwndbg_dir, "gdbinit.py"))
+
     try:
-        git_path = os.path.join(os.path.dirname(os.path.dirname(__file__)), ".git")
+        git_path = os.path.join(pwndbg_dir, ".git")
         cmd = ["git", "--git-dir", git_path, "rev-parse", "--short", "HEAD"]
 
         commit_id = subprocess.check_output(cmd, stderr=subprocess.STDOUT)