Fix Windows clippy issues (#5593)

These have been a lil bit annoying when running `cargo clippy
--all-features --all-targets` on windows

crates/eframe/src/native/file_storage.rs

@@ -58,27 +58,34 @@ fn roaming_appdata() -> Option<PathBuf> {
     extern "C" {
         fn wcslen(buf: *const u16) -> usize;
     }
-    unsafe {
+    let mut path_raw = ptr::null_mut();
-        let mut path = ptr::null_mut();
+
-        match SHGetKnownFolderPath(
+    // SAFETY: SHGetKnownFolderPath allocates for us, we don't pass any pointers to it.
+    // See https://learn.microsoft.com/en-us/windows/win32/api/shlobj_core/nf-shlobj_core-shgetknownfolderpath
+    let result = unsafe {
+        SHGetKnownFolderPath(
             &FOLDERID_RoamingAppData,
             KF_FLAG_DONT_VERIFY as u32,
             std::ptr::null_mut(),
-            &mut path,
+            &mut path_raw,
-        ) {
+        )
-            S_OK => {
+    };
-                let path_slice = slice::from_raw_parts(path, wcslen(path));
+
-                let s = OsString::from_wide(&path_slice);
+    let path = if result == S_OK {
-                CoTaskMemFree(path.cast());
+        // SAFETY: SHGetKnownFolderPath indicated success and is supposed to allocate a nullterminated string for us.
-                Some(PathBuf::from(s))
+        let path_slice = unsafe { slice::from_raw_parts(path_raw, wcslen(path_raw)) };
-            }
+        Some(PathBuf::from(OsString::from_wide(path_slice)))
-            _ => {
+    } else {
-                // Free any allocated memory even on failure. A null ptr is a no-op for `CoTaskMemFree`.
-                CoTaskMemFree(path.cast());
         None
-            }
+    };
-        }
+
-    }
+    // SAFETY:
+    // This memory got allocated by SHGetKnownFolderPath, we didn't touch anything in the process.
+    // A null ptr is a no-op for `CoTaskMemFree`, so in case this failed we're still good.
+    // https://learn.microsoft.com/en-us/windows/win32/api/combaseapi/nf-combaseapi-cotaskmemfree
+    unsafe { CoTaskMemFree(path_raw.cast()) };
+
+    path
 }
 
 #[cfg(any(not(windows), target_vendor = "uwp"))]