fix: time-picker bug (#1176)

当使用backspace删除所有字符后，输入第一个字符控制台报错，并无字符显示

Author: zkwolf

components/vc-time-picker/Header.jsx

@@ -28,7 +28,6 @@ const Header = {
     currentSelectPanel: PropTypes.string,
     focusOnOpen: PropTypes.bool,
     // onKeyDown: PropTypes.func,
-    showStr: PropTypes.bool.def(true),
     clearIcon: PropTypes.any,
   },
   data() {
@@ -70,7 +69,6 @@ const Header = {
         return;
       }
 
-      this.showStr = true;
       this.setState({
         str,
       });
@@ -192,14 +190,14 @@ const Header = {
     },
 
     getInput() {
-      const { prefixCls, placeholder, inputReadOnly, invalid, str, showStr } = this;
+      const { prefixCls, placeholder, inputReadOnly, invalid, str } = this;
       const invalidClass = invalid ? `${prefixCls}-input-invalid` : '';
       return (
         <input
           class={`${prefixCls}-input ${invalidClass}`}
           ref="input"
           onKeydown={this.onKeyDown}
-          value={showStr ? str : ''}
+          value={str}
           placeholder={placeholder}
           onInput={this.onInputChange}
           readOnly={!!inputReadOnly}

components/vc-time-picker/Panel.jsx

@@ -57,19 +57,13 @@ const Panel = {
       sValue: this.value,
       selectionRange: [],
       currentSelectPanel: '',
-      showStr: true,
     };
   },
   watch: {
     value(val) {
       if (val) {
         this.setState({
           sValue: val,
-          showStr: true,
-        });
-      } else {
-        this.setState({
-          showStr: false,
         });
       }
     },
@@ -132,7 +126,6 @@ const Panel = {
       inputReadOnly,
       sValue,
       currentSelectPanel,
-      showStr,
       $listeners = {},
     } = this;
     const clearIcon = getComponentFromProp(this, 'clearIcon');
@@ -181,7 +174,6 @@ const Panel = {
           focusOnOpen={focusOnOpen}
           onKeydown={keydown}
           inputReadOnly={inputReadOnly}
-          showStr={showStr}
           clearIcon={clearIcon}
         />
         <Combobox