Select: fix input height of mini size

packages/select/src/select.vue

@@ -495,7 +495,10 @@
           if (!this.$refs.reference) return;
           let inputChildNodes = this.$refs.reference.$el.childNodes;
           let input = [].filter.call(inputChildNodes, item => item.tagName === 'INPUT')[0];
-          input.style.height = Math.max(this.$refs.tags.clientHeight + 6, sizeMap[this.size] || 36) + 'px';
+          const tags = this.$refs.tags;
+          input.style.height = this.selected.length === 0
+            ? sizeMap[this.selectSize] + 'px'
+            : Math.max(tags ? (tags.clientHeight + 6) : 0, sizeMap[this.selectSize] || 36) + 'px';
           if (this.visible && this.emptyText !== false) {
             this.broadcast('ElSelectDropdown', 'updatePopper');
           }