fix(VAppBar): fix elevation issue when extended

[morficus]

When using hide-on-scroll in combination with extended, elevate-on-scroll would not work
as expected.

fixes #8516

Description

When using hide-on-scroll in combination with extended, elevate-on-scroll would not work as expected.

Motivation and Context

fixes #8516

How Has This Been Tested?

Unit tests
Visually

Markup:

<template>
  <v-container>
    <div>
      <v-row justify="center">
        <v-col cols="3" md="2">
          <v-switch v-model="elevateOnScroll" label="Elevate-on-scroll"></v-switch>
        </v-col>
        <v-col cols="3" md="2">
          <v-switch v-model="hideOnScroll" label="Hide-on-scroll"></v-switch>
        </v-col>

        <v-col cols="3" md="2">
          <v-switch v-model="extended" label="Extended"></v-switch>
        </v-col>
      </v-row>
      <v-card class="overflow-hidden">
        <v-app-bar
          absolute
          scroll-target="#playground-example"
          :color="color"
          :elevate-on-scroll="elevateOnScroll"
          :hide-on-scroll="hideOnScroll"
          :fade-on-scroll="fadeOnScroll"
          :fade-img-on-scroll="fadeImgOnScroll"
          :inverted-scroll="invertedScroll"
          :collapse="collapse"
          :collapse-on-scroll="collapseOnScroll"
          :shrink-on-scroll="shrinkOnScroll"
          :extended="extended"
        >
          <v-app-bar-nav-icon></v-app-bar-nav-icon>

          <template v-slot:extension>This text is in the "extension" slot</template>

          <v-toolbar-title>Title</v-toolbar-title>

          <v-spacer></v-spacer>

          <v-btn icon>
            <v-icon>search</v-icon>
          </v-btn>
        </v-app-bar>

        <v-sheet id="playground-example" class="overflow-y-auto" max-height="600">
          <v-container style="height: 1500px;"></v-container>
        </v-sheet>
      </v-card>
    </div>
  </v-container>
</template>

<script>
export default {
  data: () => ({
    elevateOnScroll: true,
    hideOnScroll: true,
    extended: true,
    color: "white"
  })
};
</script>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and breaking changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)
• I've added new examples to the kitchen (applies to new features and breaking changes in core library)

[TravisBuddy]

Hey @morficus,
Your changes look good to me!

View build log

TravisBuddy Request Identifier: fbbea660-be44-11e9-8e8d-8dee9100a8b2