fix the crash as suggested by @SpecLad

modules/java/CMakeLists.txt

@@ -134,7 +134,7 @@ endforeach()
 set(step2_depends ${step1_depends} ${scripts_gen_javadoc} ${scripts_rst_parser} ${javadoc_rst_sources} ${generated_java_sources} ${handwrittren_java_sources})
 string(REPLACE ";" "," OPENCV_JAVA_MODULES_STR "${OPENCV_JAVA_MODULES}")
 add_custom_command(OUTPUT ${documented_java_files}
-                   COMMAND ${PYTHON_EXECUTABLE} "${scripts_gen_javadoc}" --modules ${OPENCV_JAVA_MODULES_STR} "${CMAKE_CURRENT_SOURCE_DIR}/generator/src/java" "${CMAKE_CURRENT_BINARY_DIR}" 2>${CMAKE_CURRENT_BINARY_DIR}/get_javadoc_errors.log
+                   COMMAND ${PYTHON_EXECUTABLE} "${scripts_gen_javadoc}" --modules ${OPENCV_JAVA_MODULES_STR} "${CMAKE_CURRENT_SOURCE_DIR}/generator/src/java" "${CMAKE_CURRENT_BINARY_DIR}" 2> "${CMAKE_CURRENT_BINARY_DIR}/get_javadoc_errors.log"
                    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
                    DEPENDS ${step2_depends}
                   )