refactor: fix some code issues (#6945)

* Table: remove condition due to rows has been accessed prior

* Table: change el-tooltip style to object
Signed-off-by: Clark Du <clark.duxin@gmail.com>

packages/table/src/table-body.js

@@ -160,7 +160,7 @@ export default {
       const newRow = rows[data.indexOf(newVal)];
       if (oldRow) {
         removeClass(oldRow, 'current-row');
-      } else if (rows) {
+      } else {
         [].forEach.call(rows, row => removeClass(row, 'current-row'));
       }
       if (newRow) {

packages/table/src/table-column.js

@@ -290,7 +290,7 @@ export default {
       }
 
       return _self.showOverflowTooltip || _self.showTooltipWhenOverflow
-        ? <div class="cell el-tooltip" style={'width:' + (data.column.realWidth || data.column.width) + 'px'}>{ renderCell(h, data) }</div>
+        ? <div class="cell el-tooltip" style={{width: (data.column.realWidth || data.column.width) + 'px'}}>{ renderCell(h, data) }</div>
         : <div class="cell">{ renderCell(h, data) }</div>;
     };
   },