fix crash, if lexer is active in passive tab, user deletes this lexer, switches tab
fix crash, if lexer is active in passive tab, user deletes this lexer, switches tab

vhanla/CudaText,Alexey-T/CudaText,vhanla/CudaText,Alexey-T/CudaText,Alexey-T/CudaText,vhanla/CudaText,Alexey-T/CudaText,vhanla/CudaText,Alexey-T/CudaText,vhanla/CudaText,vhanla/CudaText,vhanla/CudaText,vhanla/CudaText,Alexey-T/CudaText,vhanla/CudaText,Alexey-T/CudaText,Alexey-T/CudaText,vhanla/CudaText