[cmake] Make sure ENABLE_LIBOPENJPEG is either 0 or 1

Otherwise if it was auto it gets translated to 1 for the cmakedefine boolean
which is wrong when the auto ends up meaning "i din't find it"
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f77e366..1618e1c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -158,6 +158,7 @@
 endif(ENABLE_ZLIB)
 set(USE_OPENJPEG1 FALSE)
 set(USE_OPENJPEG2 FALSE)
+set(WITH_OPENJPEG FALSE)
 if(ENABLE_LIBOPENJPEG STREQUAL "auto")
   find_package(LIBOPENJPEG)
   set(USE_OPENJPEG1 ${LIBOPENJPEG_FOUND})
@@ -176,6 +177,7 @@
   set(USE_OPENJPEG2 ${LIBOPENJPEG2_FOUND})
   set(WITH_OPENJPEG ${LIBOPENJPEG2_FOUND})
 endif()
+set(ENABLE_LIBOPENJPEG "${WITH_OPENJPEG}")
 if(ENABLE_CMS STREQUAL "auto")
   find_package(LCMS2)
   set(USE_CMS ${LCMS2_FOUND})