Crash when switching from custom renderer to standard one

[alexbruy]

When I switch from renderer created by plugin to one of the standard renderers QGIS crashes. See also http://hub.qgis.org/issues/13973

[ccrook]

Thanks for raising the issue. I think this is related to other issues which have appeared over the last year or so (first notice on Windows 64 bit platforms) seem to relate to the python SIP bindings... the C++ parts of some python objects get lost.

In this case I suspect the fix is to include a check for a null pointer on the old symbol when changing to a new in QGIS. This won't fix the python bindings issues but it will stop QGIS crashing... I guess the null pointer dereferencing should be locatable in a debugger.

[ccrook]

I don't think this is fixable within the python plugin.
Added a warning message to the plugin widget to alert user to risk..

[ccrook]

Just one other possibility to consider, which is to see if adding VectorArrowMarker to QgsSymbolLayerV2Registry.instance() makes any difference.