Fix issue of not removing dash-style on applying null value to 'stroke-dasharray'.
Fix issue of not removing dash-style on applying null value to 'stroke-dasharray'.

- The 'if' condition is modified which restricts setting of dash-array if value is found null.

AyanGhatak/redraphael,AyanGhatak/redraphael,fusioncharts/redraphael,fusioncharts/redraphael,AyanGhatak/redraphael,fusioncharts/redraphael