[v10.0/forgejo] fix: use correct input for strip slashes middleware (#7306)

**Backport:** https://codeberg.org/forgejo/forgejo/pulls/7295

- The router must use the escaped path in order to ensure correct functionality (at least, that is what they say). However `req.URL.Path` shouldn't be set to the escaped path, which is fixed in this patch.
- Simplify the logic and no longer try to use `rctx.RoutePath`, this is only useful if the middleware was placed after some routing parsing was done.
- Resolves forgejo/forgejo#7294
- Resolves forgejo/forgejo#7292
- Add unit test

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## Release notes
<!--URL:https://codeberg.org/forgejo/forgejo-->
- Bug fixes
  - [PR](https://codeberg.org/forgejo/forgejo/pulls/7295): <!--number 7295 --><!--line 0 --><!--description dXNlIGNvcnJlY3QgaW5wdXQgZm9yIHN0cmlwIHNsYXNoZXMgbWlkZGxld2FyZQ==-->use correct input for strip slashes middleware<!--description-->
<!--end release-notes-assistant-->

Co-authored-by: Gusted <postmaster@gusted.xyz>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7306
Co-authored-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
Co-committed-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>

routers/common/middleware_test.go

@@ -15,9 +15,10 @@ import (
 
 func TestStripSlashesMiddleware(t *testing.T) {
 	type test struct {
-		name         string
-		expectedPath string
-		inputPath    string
+		name               string
+		expectedPath       string
+		expectedNormalPath string
+		inputPath          string
 	}
 
 	tests := []test{
@@ -57,9 +58,16 @@ func TestStripSlashesMiddleware(t *testing.T) {
 			expectedPath: "/repo/migrate",
 		},
 		{
-			name:         "path with encoded slash",
-			inputPath:    "/user2/%2F%2Frepo1",
-			expectedPath: "/user2/%2F%2Frepo1",
+			name:               "path with encoded slash",
+			inputPath:          "/user2/%2F%2Frepo1",
+			expectedPath:       "/user2/%2F%2Frepo1",
+			expectedNormalPath: "/user2/repo1",
+		},
+		{
+			name:               "path with space",
+			inputPath:          "/assets/css/theme%20cappuccino.css",
+			expectedPath:       "/assets/css/theme%20cappuccino.css",
+			expectedNormalPath: "/assets/css/theme cappuccino.css",
 		},
 	}
 
@@ -69,7 +77,11 @@ func TestStripSlashesMiddleware(t *testing.T) {
 
 		called := false
 		r.Get("*", func(w http.ResponseWriter, r *http.Request) {
-			assert.Equal(t, tt.expectedPath, r.URL.Path)
+			if tt.expectedNormalPath != "" {
+				assert.Equal(t, tt.expectedNormalPath, r.URL.Path)
+			} else {
+				assert.Equal(t, tt.expectedPath, r.URL.Path)
+			}
 
 			rctx := chi.RouteContext(r.Context())
 			assert.Equal(t, tt.expectedPath, rctx.RoutePath)