Fixes #62096: LightmapGIData::_get_light_textures_data crash on empty image
Fixes #62096: LightmapGIData::_get_light_textures_data crash on empty image

The program crashes when trying to determine slice width/height if the
light texture is empty. This fix just returns an empty array, as if the
light texture does not exist.

ZuBsPaCe/godot,guilhermefelipecgs/godot,akien-mga/godot,Zylann/godot,BastiaanOlij/godot,Valentactive/godot,ZuBsPaCe/godot,godotengine/godot,firefly2442/godot,BastiaanOlij/godot,akien-mga/godot,BastiaanOlij/godot,pkowal1982/godot,Zylann/godot,Shockblast/godot,sanikoyes/godot,josempans/godot,akien-mga/godot,godotengine/godot,firefly2442/godot,ZuBsPaCe/godot,ZuBsPaCe/godot,ZuBsPaCe/godot,Valentactive/godot,pkowal1982/godot,josempans/godot,Shockblast/godot,godotengine/godot,Shockblast/godot,josempans/godot,firefly2442/godot,pkowal1982/godot,godotengine/godot,pkowal1982/godot,vkbsb/godot,pkowal1982/godot,pkowal1982/godot,akien-mga/godot,akien-mga/godot,sanikoyes/godot,Zylann/godot,Zylann/godot,akien-mga/godot,sanikoyes/godot,guilhermefelipecgs/godot,godotengine/godot,guilhermefelipecgs/godot,Valentactive/godot,firefly2442/godot,sanikoyes/godot,sanikoyes/godot,sanikoyes/godot,josempans/godot,ZuBsPaCe/godot,josempans/godot,vkbsb/godot,BastiaanOlij/godot,guilhermefelipecgs/godot,Valentactive/godot,godotengine/godot,guilhermefelipecgs/godot,vkbsb/godot,josempans/godot,vkbsb/godot,firefly2442/godot,firefly2442/godot,BastiaanOlij/godot,Zylann/godot,akien-mga/godot,Valentactive/godot,firefly2442/godot,josempans/godot,vkbsb/godot,vkbsb/godot,ZuBsPaCe/godot,Valentactive/godot,godotengine/godot,Shockblast/godot,Valentactive/godot,Valentactive/godot,Shockblast/godot,josempans/godot,Zylann/godot,pkowal1982/godot,Shockblast/godot,ZuBsPaCe/godot,vkbsb/godot,Shockblast/godot,Zylann/godot,guilhermefelipecgs/godot,Shockblast/godot,sanikoyes/godot,BastiaanOlij/godot,Zylann/godot,akien-mga/godot,pkowal1982/godot,BastiaanOlij/godot,godotengine/godot,vkbsb/godot,firefly2442/godot,guilhermefelipecgs/godot,guilhermefelipecgs/godot,sanikoyes/godot,BastiaanOlij/godot