GeoExtPrintForm - unnecessary alert with vector layers

[adube]

Issue

Before printing with the GeoExtPrintForm widget, if a vector layer is visible and has no features, its encoded value returned is null, thus making it as "no printable" (which is not the case) and an alert pops up.

Solution

Since vector layers are now supported by the MapFishPrint proxy, we do not need to validate it, so we simply need to not attempt to encode them.

[adube]

patch fixing the issue

[adube]

Fixed in r1057.