When opening VPL files, unknown blocks reported with "-1:-1" as location

[ypiguet-epfl]

In Aseba Studio, VPL window, when opening an aesl file with an unknown block (unknown name attribute in block element), the error message Error in XML source file at -1:-1 : cannot create block foo where foo is the block name.

Test file:

<!DOCTYPE aesl-source>
<network>
<keywords flag="true"/>
<node nodeId="1" name="thymio-II">
<toolsPlugins>
<ThymioVisualProgramming>
<vplroot xml-format-version="1">
<program advanced_mode="0">
<set>
<block type="event" name="foo"/>
</set>
</program>
</vplroot>
</ThymioVisualProgramming>
</toolsPlugins>
</node>
</network>

Suggestion: if you can't get the position of the error, suppress at -1:-1 in the error message.

[ypiguet-epfl]

Ok, it's a tiny minor issue, but "-1:-1" in a user-visible alert isn't a bug? The fix must be 1-2 lines of code, way less work than reporting it here for those who can just push a change.