Make repo installation work without .git

Some tools like jj and cog will not have .git. This change
makes it possible to run all repo commands in such setups.

Change-Id: I7f3845dc970fbaa731c31e0aa48355a4b56ed3a6
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/442821
Reviewed-by: Gavin Mak <gavinmak@google.com>
Tested-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>

repo

diff --git a/repo b/repo
index 9cedcbf..6cda136 100755
--- a/repo
+++ b/repo
@@ -124,7 +124,7 @@
 BUG_URL = "https://issues.gerritcodereview.com/issues/new?component=1370071"
 
 # increment this whenever we make important changes to this script
-VERSION = (2, 48)
+VERSION = (2, 50)
 
 # increment this if the MAINTAINER_KEYS block is modified
 KEYRING_VERSION = (2, 3)
@@ -1335,10 +1335,11 @@
 
 def _Version():
     """Show version information."""
+    git_version = ParseGitVersion()
     print("<repo not installed>")
     print(f"repo launcher version {'.'.join(str(x) for x in VERSION)}")
     print(f"       (from {__file__})")
-    print(f"git {ParseGitVersion().full}")
+    print(f"git {git_version.full}" if git_version else "git not installed")
     print(f"Python {sys.version}")
     uname = platform.uname()
     print(f"OS {uname.system} {uname.release} ({uname.version})")
@@ -1371,11 +1372,11 @@
     my_main = os.path.join(my_dir, "main.py")
     my_git = os.path.join(my_dir, ".git")
 
-    if os.path.isfile(my_main) and os.path.isdir(my_git):
+    if os.path.isfile(my_main):
         for name in ["git_config.py", "project.py", "subcmds"]:
             if not os.path.exists(os.path.join(my_dir, name)):
                 return None, None
-        return my_main, my_git
+        return my_main, my_git if os.path.isdir(my_git) else None
     return None, None