CMake: allow find_package in case liblsl is already loaded

Author: tstenner

cmake/LSLConfig.cmake

@@ -1,2 +1,8 @@
-include("${CMAKE_CURRENT_LIST_DIR}/LSLTargets.cmake")
+if(TARGET lsl AND NOT TARGET LSL::lsl)
+	add_library(LSL::lsl ALIAS lsl)
+endif()
+
+if(NOT TARGET LSL::lsl)
+	include("${CMAKE_CURRENT_LIST_DIR}/LSLTargets.cmake")
+endif()
 include("${CMAKE_CURRENT_LIST_DIR}/LSLCMake.cmake")