[perflint] Fix PERF403 panic on attribute or subscription loop variable (#19042)

## Summary

Fixes: https://github.com/astral-sh/ruff/issues/19005

## Test Plan

Reproducer from issue report plus some extra cases that would cause the
panic were added.

crates/ruff_linter/resources/test/fixtures/perflint/PERF403.py

@@ -170,3 +170,25 @@ def foo():
     v = {}
     for o,(x,)in():
         v[x,]=o
+
+
+# https://github.com/astral-sh/ruff/issues/19005
+def issue_19005_1():
+    c = {}
+    a = object()
+    for a.b in ():
+        c[a.b] = a.b
+
+
+def issue_19005_2():
+    a = object()
+    c = {}
+    for a.k, a.v in ():
+        c[a.k] = a.v
+
+
+def issue_19005_3():
+    a = [None, None]
+    c = {}
+    for a[0], a[1] in ():
+        c[a[0]] = a[1]

crates/ruff_linter/src/rules/perflint/rules/manual_dict_comprehension.rs

@@ -462,12 +462,16 @@ fn has_post_loop_references(checker: &Checker, expr: &Expr, loop_end: TextSize)
             .iter()
             .any(|expr| has_post_loop_references(checker, expr, loop_end)),
         Expr::Name(name) => {
-            let target_binding = checker
+            let Some(target_binding) = checker
                 .semantic()
                 .bindings
                 .iter()
                 .find(|binding| name.range() == binding.range)
-                .expect("for-loop target binding must exist");
+            else {
+                // no binding in for statement => err on the safe side and make the checker skip
+                // e.g., `for foo[0] in bar:` or `for foo.bar in baz:`
+                return true;
+            };
 
             target_binding
                 .references()

crates/ruff_linter/src/rules/perflint/snapshots/ruff_linter__rules__perflint__tests__preview__PERF403_PERF403.py.snap

@@ -374,3 +374,6 @@ PERF403.py:172:9: PERF403 [*] Use a dictionary comprehension instead of a for-lo
 171     |-    for o,(x,)in():
 172     |-        v[x,]=o
     170 |+    v = {x: o for o,(x,) in ()}
+173 171 | 
+174 172 | 
+175 173 | # https://github.com/astral-sh/ruff/issues/19005