add null check in MeshInstance::_mesh_changed()
add null check in MeshInstance::_mesh_changed()

Shockblast/godot,Faless/godot,Shockblast/godot,Faless/godot,DmitriySalnikov/godot,Shockblast/godot,Zylann/godot,Shockblast/godot,guilhermefelipecgs/godot,Faless/godot,guilhermefelipecgs/godot,BastiaanOlij/godot,ZuBsPaCe/godot,DmitriySalnikov/godot,ZuBsPaCe/godot,BastiaanOlij/godot,honix/godot,MarianoGnu/godot,godotengine/godot,josempans/godot,vnen/godot,vnen/godot,Zylann/godot,firefly2442/godot,akien-mga/godot,godotengine/godot,firefly2442/godot,ZuBsPaCe/godot,akien-mga/godot,ZuBsPaCe/godot,Zylann/godot,josempans/godot,Zylann/godot,vnen/godot,pkowal1982/godot,guilhermefelipecgs/godot,BastiaanOlij/godot,josempans/godot,guilhermefelipecgs/godot,firefly2442/godot,Valentactive/godot,ZuBsPaCe/godot,pkowal1982/godot,firefly2442/godot,DmitriySalnikov/godot,Valentactive/godot,Shockblast/godot,DmitriySalnikov/godot,Valentactive/godot,godotengine/godot,akien-mga/godot,firefly2442/godot,pkowal1982/godot,josempans/godot,sanikoyes/godot,vkbsb/godot,vnen/godot,Zylann/godot,sanikoyes/godot,Zylann/godot,akien-mga/godot,BastiaanOlij/godot,pkowal1982/godot,sanikoyes/godot,Valentactive/godot,DmitriySalnikov/godot,guilhermefelipecgs/godot,MarianoGnu/godot,vkbsb/godot,josempans/godot,guilhermefelipecgs/godot,honix/godot,MarianoGnu/godot,Valentactive/godot,firefly2442/godot,MarianoGnu/godot,vkbsb/godot,vnen/godot,vkbsb/godot,Shockblast/godot,akien-mga/godot,pkowal1982/godot,ZuBsPaCe/godot,godotengine/godot,Faless/godot,Zylann/godot,Shockblast/godot,vkbsb/godot,vnen/godot,sanikoyes/godot,ZuBsPaCe/godot,honix/godot,pkowal1982/godot,godotengine/godot,Shockblast/godot,DmitriySalnikov/godot,MarianoGnu/godot,guilhermefelipecgs/godot,Zylann/godot,Faless/godot,godotengine/godot,guilhermefelipecgs/godot,sanikoyes/godot,sanikoyes/godot,BastiaanOlij/godot,sanikoyes/godot,vnen/godot,vkbsb/godot,BastiaanOlij/godot,godotengine/godot,akien-mga/godot,godotengine/godot,Valentactive/godot,vkbsb/godot,vnen/godot,BastiaanOlij/godot,pkowal1982/godot,Valentactive/godot,MarianoGnu/godot,MarianoGnu/godot,sanikoyes/godot,firefly2442/godot,Valentactive/godot,josempans/godot,honix/godot,DmitriySalnikov/godot,Faless/godot,firefly2442/godot,Faless/godot,honix/godot,akien-mga/godot,josempans/godot,josempans/godot,vkbsb/godot,MarianoGnu/godot,BastiaanOlij/godot,ZuBsPaCe/godot,pkowal1982/godot,akien-mga/godot,Faless/godot,honix/godot