Fixed CMake issue with FFMPEG videoio configuration

modules/videoio/CMakeLists.txt

@@ -18,13 +18,11 @@ endif()
 
 set(videoio_hdrs
     ${CMAKE_CURRENT_LIST_DIR}/src/precomp.hpp
-    ${CMAKE_CURRENT_LIST_DIR}/src/cap_ffmpeg_impl.hpp
     )
 
 set(videoio_srcs
     ${CMAKE_CURRENT_LIST_DIR}/src/cap.cpp
     ${CMAKE_CURRENT_LIST_DIR}/src/cap_images.cpp
-    ${CMAKE_CURRENT_LIST_DIR}/src/cap_ffmpeg.cpp
     )
 
 file(GLOB videoio_ext_hdrs
@@ -111,6 +109,8 @@ if(HAVE_XIMEA)
 endif(HAVE_XIMEA)
 
 if(HAVE_FFMPEG)
+  list(APPEND videoio_hdrs ${CMAKE_CURRENT_LIST_DIR}/src/cap_ffmpeg_impl.hpp)
+  list(APPEND videoio_srcs ${CMAKE_CURRENT_LIST_DIR}/src/cap_ffmpeg.cpp)
   if(UNIX AND BZIP2_LIBRARIES)
     list(APPEND VIDEOIO_LIBRARIES ${BZIP2_LIBRARIES})
   endif()