Apply suggestions from code review

Co-authored-by: Jakub Beránek <[email protected]>

Author: lolbinarycat

src/tools/tidy/src/lib.rs

@@ -169,7 +169,6 @@ pub fn files_modified_batch_filter<T>(
         None => {
             eprintln!("warning: failed to run `git diff` to check for changes");
             eprintln!("warning: assuming all files are modified");
-            return;
         }
     }
 }
@@ -178,7 +177,7 @@ pub fn files_modified_batch_filter<T>(
 pub fn files_modified(ci_info: &CiInfo, pred: impl Fn(&str) -> bool) -> bool {
     let mut v = vec![()];
     files_modified_batch_filter(ci_info, &mut v, |_, p| pred(p));
-    v.is_empty()
+    !v.is_empty()
 }
 
 pub mod alphabetical;