Fix OpenJPEG target handling in DCMTKConfig.cmake

When DCMTK is built with OpenJPEG support, DCMTKTargets.cmake contains
INTERFACE_LINK_LIBRARIES entries that reference the imported target
openjp2. If a consuming project includes DCMTKConfig.cmake without
previously finding OpenJPEG, CMake errors out because the openjp2
target does not exist.

Fix by calling find_package(OpenJPEG) in DCMTKConfig.cmake before the
DCMTK targets are imported, but only when DCMTK was built with
OpenJPEG support and the openjp2 target has not already been defined.
This ensures the openjp2 target is available when DCMTKTargets.cmake
is processed, without forcing projects that already found OpenJPEG
themselves to find it again.

Author: lassoan

CMake/DCMTKConfig.cmake.in

@@ -109,6 +109,10 @@ SET_AND_CHECK(DCMTK_TARGETS "@PACKAGE_DCMTK_CMKDIR_CONFIG@/DCMTKTargets.cmake")
 # Compatibility: This variable is deprecated
 set(DCMTK_INCLUDE_DIR ${DCMTK_INCLUDE_DIRS})
 
+if(DCMTK_WITH_OPENJPEG AND NOT TARGET openjp2)
+  find_package(OpenJPEG CONFIG QUIET)
+endif()
+
 if(NOT DCMTK_TARGETS_IMPORTED)
   set(DCMTK_TARGETS_IMPORTED 1)
   include(${DCMTK_TARGETS})