ignore: squash noisy error message

We should not assume that the commondir file actually exists. If it
doesn't, then just move on. This otherwise emits an error message when
searching normal submodules, which is not OK.

This regression was introduced in #1446.

Fixes #1520

CHANGELOG.md

@@ -1,3 +1,14 @@
+12.0.1 (TBD)
+============
+ripgrep 12.0.1 is a small patch release that includes a couple minor bug fixes.
+These bug fixes address regressions introduced in the 12.0.0 release.
+
+Bug fixes:
+
+* [BUG #1520](https://github.com/BurntSushi/ripgrep/issues/1520):
+  Don't emit spurious error messages in git repositories with submodules.
+
+
 12.0.0 (2020-03-15)
 ===================
 ripgrep 12 is a new major version release of ripgrep that contains many bug

crates/ignore/src/dir.rs

@@ -310,7 +310,7 @@ impl Ignore {
             git_global_matcher: self.0.git_global_matcher.clone(),
             git_ignore_matcher: gi_matcher,
             git_exclude_matcher: gi_exclude_matcher,
-            has_git: has_git,
+            has_git,
             opts: self.0.opts,
         };
         (ig, errs.into_error_option())
@@ -817,9 +817,7 @@ fn resolve_git_commondir(
     let git_commondir_file = || real_git_dir.join("commondir");
     let file = match File::open(git_commondir_file()) {
         Ok(file) => io::BufReader::new(file),
-        Err(err) => {
-            return Err(Some(Error::Io(err).with_path(git_commondir_file())));
-        }
+        Err(_) => return Err(None),
     };
     let commondir_line = match file.lines().next() {
         Some(Ok(line)) => line,