SaveTool: add a fallback if there are no profile backups.

The table formatting was messed up when there were no backups, so I'm
working around it by... not displaying the table.

src/SaveTool/SaveTool_ProfileManager.cpp

@@ -225,7 +225,10 @@ auto SaveTool::drawBackupListPopup() -> ImGuiID {
         ImGui::EndTable();
     }
 
-    if(ImGui::BeginTable("##Backups", 4,
+    if(_profileManager->backups().empty()) {
+        ImGui::TextDisabled("No backups were found.");
+    }
+    else if(ImGui::BeginTable("##Backups", 4,
                          ImGuiTableFlags_BordersOuter|ImGuiTableFlags_RowBg))
     {
         ImGui::TableSetupScrollFreeze(0, 1);