CMake: Always copy assets to build directory, fixes example: $ make run

CMakeLists.txt

@@ -69,9 +69,10 @@ add_subdirectory("src")
 # ------------------------------------------
 # Assets target
 
-add_custom_target(${ENGINE}-assets ALL
+add_custom_target(${ENGINE}-assets
 	COMMAND ${CMAKE_COMMAND} -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/copy-assets.cmake
 	WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
+add_dependencies(${ENGINE} ${ENGINE}-assets)
 
 # ------------------------------------------
 # Examples target