Group header with columns which width is defined as number throws an exception

[npaunov]

Description

Group Header causes an error when the columns' width is a number

• igniteui-angular version: 6.2.x
• browser: all

Steps to reproduce

1. Go to the dev demos Grid Cell Styling
2. Add group header e.g.:

<igx-column-group header="Group Header 1">
<igx-column *ngFor="let c of columns" [field]="c.field" [header]="c.field" [width]="c.width"
                    [movable]="true" [groupable]="true"
                    [resizable]="true" [sortable]="true"   [filterable]="true"
                    [editable]="true" [cellClasses]="c.cellClasses">
   </igx-column>
 </igx-column-group>

3. Run the sample

Result

The columns are not shown and there is an error in the console:
"ERROR TypeError: val.width.indexOf is not a function"

Expected result

The columns are shown with multi column header and there is no error.

Note:

In projects\igniteui-angular\src\lib\grids\column.component.ts

the check expects a string although the columns widths in the sample are defined as numbers. Perhaps a cast to string can be added before the '%' check