fix(core): Fix #4776 scrollTo doesn't work with higher rowHeight

Change the way pixelsToSeeRow variable is calculated. This way
is possible to have different heights for rows and column headers.

Author: imbalind

Diff for: src/js/core/factories/Grid.js

@@ -2332,7 +2332,7 @@ angular.module('ui.grid')
         //}
 
         // This is the minimum amount of pixels we need to scroll vertical in order to see this row.
-        var pixelsToSeeRow = ((seekRowIndex + 1) * self.options.rowHeight);
+        var pixelsToSeeRow = (seekRowIndex * self.options.rowHeight + self.headerHeight);
 
         // Don't let the pixels required to see the row be less than zero
         pixelsToSeeRow = (pixelsToSeeRow < 0) ? 0 : pixelsToSeeRow;