Fixed bug that allowed the asset browser's back button to leave the project's assets directory

docs/tasks/Bugs.todo

@@ -1,6 +1,6 @@
 
 High Importance:
-    ☐ AssetBrowser back button does not stop at the asset root directory @high
+    ✔ AssetBrowser back button does not stop at the asset root directory @high @done(22-07-05 13:53)
     ✔ Editor does not get absolute paths from the file browser - replace with NFD dialogs @critical @done(22-05-20 18:36)
     ✔ The Map Editor does not get the tile maps when a project is opened @high @done (3/3/2022, 2:47:41 PM)
     ✔ Tile Set IDs (as opposed to the Asset ID) is not saved or loaded yet @high @done (3/11/2022, 2:10:30 PM)

src/run_modes/editor/panels/asset_browser.cpp

@@ -144,7 +144,12 @@ namespace editor
                 ImGui::PushFont(GUI::GetInstance().GetFont(GuiFont::FONT_ROBO_SMALL));
                 ImGui::TextUnformatted(mpEditor->GetProject()->MakeRelativeToAssets(mSelectedDir, true).string().c_str());
                 ImGui::PopFont();
-                if (ImGui::Button("Back"))
+
+                // Prevent the back button from leaving the projects asset directory
+                std::string parent = mSelectedDir.parent_path().lexically_normal().string();
+                std::string assets_str = mpEditor->GetProject()->GetAssetDirectory().lexically_normal().string();
+                size_t loc = parent.find(assets_str);
+                if (ImGui::Button("Back") && (loc != std::string::npos))
                 {
                     mSelectedDir = mSelectedDir.parent_path();
                     mSyncTree = true;