Ticket #3995: adding checks that fix problems with invalid GGB files

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31152 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Tiny fixes for Envelope

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31153 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
properties error (BarA)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31154 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Equality case fixed in #2551 (broken in previous commits)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31156 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
#3993 fixed in desktop

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31157 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
properties errors (Fixed -> fixed)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31158 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
make sure angle label hidden when angle not drawn eg 0, 360

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31159 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
use correct default for right-drag erase (Pen Tool)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31160 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Envelopes: Fix to handle single points as output

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31161 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e