message: Fix for vue: Button "Next" and "Complete" doesn't work if end-user has fixed an error in the the focused question
diff: :value="survey.pagePrevText"
  v-show="!survey.isFirstPage && survey.isShowPrevButton"
  :class="survey.cssNavigationPrev"
  + @mousedown="buttonMouseDown"
  @click="prevPage"
  />
  <input
  :value="survey.pageNextText"
  v-show="!survey.isLastPage"
  :class="survey.cssNavigationNext"
  + @mousedown="nextButtonMouseDown"
  @click="nextPage"
  />
  <input
  :value="survey.previewText"
  v-show="survey.isLastPage"
  :class="survey.cssNavigationPreview"
  + @mousedown="buttonMouseDown"
  @click="showPreview"
  />
  <input
  :value="survey.completeText"
  v-show="survey.isLastPage"
  :class="survey.cssNavigationComplete"
  + @mousedown="buttonMouseDown"
  @click="completeLastPage"
  />
  </div>
  import Vue from "vue";
  import { Component, Prop } from "vue-property-decorator";
  import { SurveyModel } from "../survey";
  +import { PageModel } from "../page";
  @Component
  export class Navigation extends Vue {
  + private mouseDownPage: PageModel;
  @Prop survey: SurveyModel;
  @Prop css: any;
  + nextButtonMouseDown() {
  + this.mouseDownPage = this.survey.currentPage;
  + return this.survey.navigationMouseDown();
  + }
  + buttonMouseDown() {
  + return this.survey.navigationMouseDown();
  + }
  prevPage() {
  this.survey.prevPage();
  }
  nextPage() {
  + if (!!this.mouseDownPage && this.mouseDownPage !== this.survey.currentPage)
  + return;
  + this.mouseDownPage = null;
  this.survey.nextPage();
  }
  completeLastPage() {
  