rust-narrow: fix loop that never loops

This was caught by `clippy`. I guess the narrow tests leave something to be
desired, since this previously only checked the first valid pattern.

rust/hg-core/src/narrow.rs

@@ -100,12 +100,12 b' fn validate_patterns(patterns: &[u8]) ->'
         }
         for prefix in VALID_PREFIXES.iter() {
             if pattern.starts_with(prefix.as_bytes()) {
-                break;
+                return Ok(());
+            }
             }
             return Err(SparseConfigError::InvalidNarrowPrefix(
                 pattern.to_owned(),
             ));
         }
-    }
     Ok(())
 }

tests/test-narrow-clone.t

@@ -28,6 +28,18 b' Only path: and rootfilesin: pattern pref'
   (narrow patterns must begin with one of the following: path:, rootfilesin:)
   [255]
 
+rootfilesin: patterns work
+
+  $ hg clone --narrow ssh://user@dummy/master rootfilesin --noupdate --include 'rootfilesin:dir'
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 0 changes to 0 files
+  new changesets 26ce255d5b5d
+  $ hg tracked -R rootfilesin
+  I rootfilesin:dir
+
 narrow clone a file, f10
 
   $ hg clone --narrow ssh://user@dummy/master narrow --noupdate --include "dir/src/f10"