Check if lrelease is working before trying to use it

On some systems, there is a /usr/bin/lrelease wrapper even if the real
lrelease program is not installed. So let's try to execute lrelease
after it has been found by find_program to see if it is really working.

translations/CMakeLists.txt

@@ -34,6 +34,12 @@ find_program(LRELEASE lrelease)
 if(LRELEASE STREQUAL "LRELEASE-NOTFOUND")
   set(ts_files "")
   message(WARNING "lrelease program not found, translation files not built")
+else()
+  execute_process(COMMAND ${LRELEASE} -version
+    RESULT_VARIABLE lrelease_ret)
+  if(NOT lrelease_ret EQUAL "0")
+    set(ts_files "")
+    message(WARNING "lrelease program not working, translation files not built")
   else()
     file(GLOB ts_files RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}" *.ts)
     foreach(ts_file ${ts_files})
@@ -44,6 +50,7 @@ else()
         WORKING_DIRECTORY "${CMAKE_CURRENT_BIN_DIR}")
     endforeach()
   endif()
+endif()
 
 string(REPLACE ".ts" ".qm" qm_files "${ts_files}")