Have git verify the repository

Rather than simply check for the presence of `.git` when `git-save`
exists, run `git rev-parse --is-inside-work-tree` and replace the `.git`
directory when it returns an error. This will fix corrupted `.git`
directories left over from previous builds, as well as missing `.git`
directories.

Author: theory

PGBuild/SCM.pm

@@ -1074,9 +1074,15 @@ sub _update_target
 	my @gitlog;
 
 	# If a run crashed during copy_source(), repair.
-	if (-d "./git-save" && !-d "$target/.git")
+	if (-d "./git-save")
 	{
-		move "./git-save", "$target/.git";
+		system(qq{git -C $target rev-parse --is-inside-work-tree > $devnull 2>&1});
+		if ($?)
+		{
+			require File::Path;
+			File::Path::remove_tree("$target/.git");
+			move "./git-save", "$target/.git";
+		}
 	}
 
 	chdir $target;