Avoid panic when comment is preceded by Unicode (#9331)

Closes https://github.com/astral-sh/ruff/issues/9328.

crates/ruff_linter/resources/test/fixtures/pylint/empty_comment.py

@@ -51,3 +51,8 @@ x = 1
 #
 ##
 #
+
+# This should be removed.
+
+α = 1
+α#

crates/ruff_linter/src/rules/pylint/rules/empty_comment.rs

@@ -88,10 +88,13 @@ fn empty_comment(range: TextRange, locator: &Locator) -> Option<Diagnostic> {
         .slice(TextRange::new(line.start(), first_hash_col))
         .char_indices()
         .rev()
-        .find(|&(_, c)| !is_python_whitespace(c) && c != '#')
-        .map(|(last_non_whitespace_non_comment_col, _)| {
-            // SAFETY: (last_non_whitespace_non_comment_col + 1) <= first_hash_col
-            TextSize::try_from(last_non_whitespace_non_comment_col).unwrap() + TextSize::new(1)
+        .find_map(|(index, char)| {
+            if is_python_whitespace(char) || char == '#' {
+                None
+            } else {
+                // SAFETY: <= first_hash_col
+                Some(TextSize::try_from(index + char.len_utf8()).unwrap())
+            }
         });
 
     Some(

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLR2044_empty_comment.py.snap

@@ -115,4 +115,19 @@ empty_comment.py:45:1: PLR2044 [*] Line with empty comment
 47 46 | # These should also be removed.
 48 47 | 
 
+empty_comment.py:58:2: PLR2044 [*] Line with empty comment
+   |
+57 | α = 1
+58 | α#
+   |  ^ PLR2044
+   |
+   = help: Delete the empty comment
+
+ℹ Safe fix
+55 55 | # This should be removed.
+56 56 | 
+57 57 | α = 1
+58    |-α#
+   58 |+α
+